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Norethisterone, also known as norethindrone and sold under many brand names, is a
progestin A progestogen, also referred to as a progestagen, gestagen, or gestogen, is a type of medication which produces effects similar to those of the natural product, natural female sex hormone progesterone in the body. A progestin is a ''synthetic co ...
medication used in
birth control pill The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. The pill contains two important hormones: progest ...
s,
menopausal hormone therapy Hormone replacement therapy (HRT), also known as menopausal hormone therapy or postmenopausal hormone therapy, is a form of hormone therapy used to treat symptoms associated with female menopause. These symptoms can include hot flashes, vagina ...
, and for the treatment of
gynecological disorder Gynaecology or gynecology (see spelling differences) is the area of medicine that involves the treatment of women's diseases, especially those of the reproductive organs. It is often paired with the field of obstetrics, forming the combined area ...
s. The medication is available in both low-dose and high-dose formulations and both alone and in combination with an
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
. It is used
by mouth Oral administration is a route of administration where a substance is taken through the mouth. Per os abbreviated to P.O. is sometimes used as a direction for medication to be taken orally. Many medications are taken orally because they are i ...
or, as
norethisterone enanthate Norethisterone enanthate (NETE), also known as norethindrone enanthate, is a form of hormonal birth control which is used to prevent pregnancy in women. It is used both as a form of progestogen-only injectable birth control and in combined inject ...
, by injection into muscle.
Side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
s of norethisterone include
menstrual irregularities Irregular menstruation is a menstrual disorder whose manifestations include irregular cycle lengths as well as metrorrhagia (vaginal bleeding between expected periods). The possible causes of irregular menstruation may vary. The common factors of ...
,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
s,
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
,
breast tenderness Breast pain is the symptom of discomfort in either one or both breasts. Pain in both breasts is often described as ''breast tenderness'', is usually associated with the menstrual period and is not serious. Pain that involves only one part of a br ...
, mood changes,
acne Acne, also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, black ...
, increased hair growth.https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/018405s023lbl.pdf Norethisterone is a progestin, or a synthetic
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. ...
, and hence is an
agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...
of the
progesterone receptor The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone. In humans, PR is encoded by a single ''PGR'' gene resid ...
, the
biological target A biological target is anything within a living organism to which some other entity (like an endogenous ligand or a drug) is directed and/or binds, resulting in a change in its behavior or function. Examples of common classes of biological targets ...
of progestogens like
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
. It has weak
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
ic and
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
ic activity, mostly at high dosages, and no other important
hormonal A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required fo ...
activity. Norethisterone was discovered in 1951 and was one of the first progestins to be developed. It was first introduced for medical use on its own in 1957 and was introduced in combination with an estrogen for use as a birth control pill in 1963. It is sometimes referred to as a "first-generation" progestin. Along with
desogestrel Desogestrel is a progestin medication which is used in birth control pills for women. It is also used in the treatment of menopausal symptoms in women. The medication is available and used alone or in combination with an estrogen. It is taken ...
, it is one of the only progestins that is widely available as a progestogen-only "mini pill" for birth control. Norethisterone is marketed widely throughout the world. It is available as a
generic medication A generic drug is a pharmaceutical drug that contains the same chemical substance as a drug that was originally protected by chemical patents. Generic drugs are allowed for sale after the patents on the original drugs expire. Because the active ch ...
. In 2020, it was the 137th most commonly prescribed medication in the United States, with more than 4million prescriptions. It is on the
World Health Organization's List of Essential Medicines The WHO Model List of Essential Medicines (aka Essential Medicines List or EML), published by the World Health Organization (WHO), contains the medications considered to be most effective and safe to meet the most important needs in a health ...
.


Medical uses

Norethisterone is used as a hormonal contraceptive in combination with an estrogen – usually
ethinylestradiol Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. In the past, EE was widely used for various indications such as the treatment of menopausal symptoms, gynecological disord ...
(EE) – in
combined oral contraceptive pill The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. The pill contains two important hormones: progest ...
s and alone in
progestogen-only pill Progestogen-only pills or progestin-only pills (POP) are contraceptive pills that contain only synthetic progestogens (progestins) and do not contain estrogen (medication), estrogen. They are colloquially known as mini pills. Although such pills ...
s. Another medical use of norethisterone is to alleviate
endometriosis Endometriosis is a disease of the female reproductive system in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus, grow outside the uterus. Most often this is on the ovaries, f ...
related pain. In fact, 50% of patients who received medical or surgical treatment for endometriosis-related pelvic pain have benefited from
progestin A progestogen, also referred to as a progestagen, gestagen, or gestogen, is a type of medication which produces effects similar to those of the natural product, natural female sex hormone progesterone in the body. A progestin is a ''synthetic co ...
therapy. This could be due to the fact that norethisterone induces endometrial proliferation during secretory phase, which has been shown to alleviate endometrial pain complaints. Another way in which norethisterone may be acting to reduce endometrial pain is via inhibition of
ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized ...
. Endometriosis pain and discomfort is worse during ovulation.


Contraindications

High-dose (10 mg/day) norethisterone has been associated with
hepatic veno-occlusive disease Hepatic veno-occlusive disease (VOD) or veno-occlusive disease with immunodeficiency is a potentially life-threatening condition in which some of the small veins in the liver are obstructed. It is a complication of high-dose chemotherapy given bef ...
, and because of this adverse effect, norethisterone should not be given to patients undergoing
allogeneic Allotransplant (''allo-'' meaning "other" in Greek) is the transplantation of cells, tissues, or organs to a recipient from a genetically non-identical donor of the same species. The transplant is called an allograft, allogeneic transplant, o ...
bone marrow transplantation Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...
, as it has been associated with substantially lower one-year survival post-transplantation.


Side effects

At contraceptive and hormone replacement dosages (0.35 to 1 mg/day), norethisterone has essentially progestogenic
side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
s only. In most clinical studies of norethisterone for contraception or menopausal hormone therapy, the drug has been combined with an estrogen, and for this reason, it is difficult to determine which of the side effects were caused by norethisterone and which of them were caused by estrogen in such research. However, NETE, an intramuscularly administered prodrug of norethisterone which is used as a long-acting contraceptive, is used without an estrogen, and hence can be employed as a surrogate for norethisterone in terms of understanding its effects and
tolerability Tolerability refers to the degree to which overt adverse effects of a drug can be tolerated by a patient. Tolerability of a particular drug can be discussed in a general sense, or it can be a quantifiable measurement as part of a clinical study. U ...
. In clinical studies, the most common side effect with NETE has been
menstrual disturbance A menstrual disorder is characterized as any abnormal condition with regards to a person's menstrual cycle. There are many different types of menstrual disorders that vary with signs and symptoms, including pain during menstruation, heavy bleeding, ...
s, including prolonged bleeding or spotting and
amenorrhea Amenorrhea is the absence of a menstrual period in a woman of reproductive age. Physiological states of amenorrhoea are seen, most commonly, during pregnancy and lactation (breastfeeding). Outside the reproductive years, there is absence of menses ...
. Other side effects have included periodic
abdominal bloating Abdominal bloating (or simply bloating) is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, press ...
and
breast tenderness Breast pain is the symptom of discomfort in either one or both breasts. Pain in both breasts is often described as ''breast tenderness'', is usually associated with the menstrual period and is not serious. Pain that involves only one part of a br ...
, both of which are thought to be due to water retention and can be relieved with
diuretic A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics in ...
s. There has been no association with
weight gain Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition. Description Weight gain occurs wh ...
, and
blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
,
blood clotting Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanis ...
, and
glucose tolerance Prediabetes is a component of the metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesit ...
have all remained normal. However, a decrease in cholesterol has been observed. At high doses (5 to 60 mg/day), for instance those used in the treatment of gynecological disorders, norethisterone can cause
hypogonadism Hypogonadism means diminished functional activity of the gonads—the testes or the ovaries—that may result in diminished production of sex hormones. Low androgen (e.g., testosterone) levels are referred to as hypoandrogenism and low estrogen ...
due to its antigonadotropic effects and can have estrogenic and weak androgenic side effects. High doses of NETA (10 mg/day) have been associated with abnormal
liver function tests Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin ti ...
, including significant elevations in liver enzymes. These
liver enzyme Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin tim ...
s included
lactate dehydrogenase Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells. LDH catalyzes the conversion of lactate to pyruvate and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that transfers a hydride from on ...
and glutamate pyruvate transaminase. Although they were described as having no clinical relevance, the elevated liver enzymes associated with NETA may have precluded its further development for male hormonal contraception.


Androgenic

Due to its weak androgenic activity, norethisterone can produce androgenic
side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
s such as
acne Acne, also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, black ...
,
hirsutism Hirsutism is excessive body hair on parts of the body where hair is normally absent or minimal. The word is from early 17th century: from Latin ''hirsutus'' meaning "hairy". It usually refers to a "male" pattern of hair growth in a female that ...
, and
voice change ' A voice change or voice mutation, sometimes referred to as a voice break or voice crack, commonly refers to the deepening of the voice of men as they reach puberty. Before puberty, both sexes have roughly similar vocal pitch, but during puberty ...
s of slight severity in some women at high dosages (e.g., 10 to 40 mg/day). This is notably not the case with
combined oral contraceptive The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. The pill contains two important hormones: progesti ...
s that contain norethisterone and EE, however. Such formulations contain low dosages of norethisterone (0.35 to 1 mg/day) in combination with
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
and are actually associated with improvement in acne symptoms. In accordance, they are in fact approved by the for the treatment of acne in women in the United States. The improvement in acne symptoms is believed to be due to a 2- to 3-fold increase in
sex hormone-binding globulin Sex hormone-binding globulin (SHBG) or sex steroid-binding globulin (SSBG) is a glycoprotein that binds to androgens and estrogens. When produced by the Sertoli cells in the seminiferous tubules of the testis, it has also been called androgen ...
(SHBG) levels and a consequent decrease in free
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
levels caused by EE, which results in an overall decrease in androgenic signaling in the body. The
sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...
s are highly androgen-sensitive and their size and activity are potential markers of androgenic effect. A high dosage of 20 mg/day norethisterone or NETA has been found to significantly stimulate the sebaceous glands, whereas lower dosages of 5 mg/day and 2.5 mg/day norethisterone and NETA, respectively, did not significantly stimulate sebum production and were consequently regarded as devoid of significant androgenicity. Conversely, dosages of norethisterone of 0.5 to 3 mg/day have been found to dose-dependently decrease SHBG levels (and hence to suppress hepatic SHBG production), which is another highly sensitive marker of androgenicity. A large clinical study of high to very high oral dosages of norethisterone (10 to 40 mg/day) administered for prolonged periods of time (4 to 35 weeks) to prevent
miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
in
pregnant Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occur ...
women found that 5.5% of the women experienced mild androgenic side effects such as mild
voice change ' A voice change or voice mutation, sometimes referred to as a voice break or voice crack, commonly refers to the deepening of the voice of men as they reach puberty. Before puberty, both sexes have roughly similar vocal pitch, but during puberty ...
s (
hoarseness A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice, can be associated with a feeling of unease or scratchiness in the ...
), acne, and
hirsutism Hirsutism is excessive body hair on parts of the body where hair is normally absent or minimal. The word is from early 17th century: from Latin ''hirsutus'' meaning "hairy". It usually refers to a "male" pattern of hair growth in a female that ...
and that 18.3% of female infants born to the mothers showed, in most cases only slight,
virilization Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens. Virilization is most commonly used in three medical and biology ...
of the
genital A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
s. Maternal androgenic symptoms occurred most often in women who received a dosage of norethisterone of 30 mg/day or more for a period of 15 weeks or longer. In the female infants who experienced virilization of the genitals, the sole manifestation in 86.7% of the cases was varied but almost always slight enlargement of the clitoris. In the remaining 13.3% of the affected cases, marked clitoral enlargement and partial fusion of the labioscrotal folds occurred. The dosages used in these cases were 20 to 40 mg/day. In a letter to the editor on the topic of virilization caused by high dosages of NETA in women, a physician expressed that they had not observed the "slightest evidence of virilization" and that there had "certainly been no hirsutism nor any voice changes" in 55 women with advanced breast cancer that they had treated with 30 to 60 mg/day norethisterone for up to six months. High-dosage norethisterone has been used to suppress
menstruation Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of hor ...
in women with severe
intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation,Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signifi ...
who were incapable of handling their own menses. A study of 118 nulliparous women treated with 5 mg/day norethisterone for a period of 2 to 30 months found that the drug was effective in producing
amenorrhea Amenorrhea is the absence of a menstrual period in a woman of reproductive age. Physiological states of amenorrhoea are seen, most commonly, during pregnancy and lactation (breastfeeding). Outside the reproductive years, there is absence of menses ...
in 86% of the women, with
breakthrough bleeding Intermenstrual bleeding, previously known as metrorrhagia, is uterine bleeding at irregular intervals, particularly between the expected menstrual periods. It is a cause of vaginal bleeding. In some women, menstrual spotting between periods occ ...
occurring in the remaining 14%. Side effects including
weight gain Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition. Description Weight gain occurs wh ...
,
hirsutism Hirsutism is excessive body hair on parts of the body where hair is normally absent or minimal. The word is from early 17th century: from Latin ''hirsutus'' meaning "hairy". It usually refers to a "male" pattern of hair growth in a female that ...
,
acne Acne, also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, black ...
,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
,
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
, and
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...
all did not appear to increase in incidence and no "disturbing side effects" were noted in any of the women. Another study of 5 mg/day norethisterone in 132 women also made no mention of androgenic side effects. These findings suggest little to no risk of androgenic side effects with norethisterone at a dosage of 5 mg/day. A study of 194 women treated with 5 to 15 mg/day NETA for a median duration of 13 months of therapy to suppress symptoms of
endometriosis Endometriosis is a disease of the female reproductive system in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus, grow outside the uterus. Most often this is on the ovaries, f ...
observed no side effects in 55.2% of patients, weight gain in 16.1%, acne in 9.9%,
mood lability In medicine and psychology, emotional lability is a sign or symptom typified by exaggerated changes in mood or affect in quick succession. Sometimes the emotions expressed outwardly are very different from how the person feels on the inside. Thes ...
in 8.9%,
hot flash Hot flashes (also known as hot flushes) are a form of flushing, often caused by the changing hormone levels that are characteristic of menopause. They are typically experienced as a feeling of intense heat with sweating and rapid heartbeat, and ...
es in 8.3%, and voice deepening in two women (1.0%).


Estrogenic

Norethisterone is weakly
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
ic (via conversion into its
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
EE), and for this reason, it has been found at high dosages to be associated with high rates of estrogenic side effects such as
breast enlargement Breast enlargement is the enlargement of the breasts. It may occur naturally as in mammoplasia or may occur artificially through active intervention. Many women regard their breasts, which are female secondary sex characteristics, as important to t ...
in women and
gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse (1 ...
in men, but also with improvement of
menopausal Menopause, also known as the climacteric, is the time in women's lives when Menstruation, menstrual periods stop permanently, and they are no longer fertility, able to bear children. Menopause usually occurs between the age of 47 and 54. Medic ...
symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...
s in postmenopausal women. It has been suggested that very high dosages (e.g., 40 mg/day, which are sometimes used in clinical practice for various indications) of NETA (and by extension norethisterone) may result in an increased risk of
venous thromboembolism Venous thrombosis is blockage of a vein caused by a thrombus (blood clot). A common form of venous thrombosis is deep vein thrombosis (DVT), when a blood clot forms in the deep veins. If a thrombus breaks off (embolizes) and flows to the lungs to ...
(VTE) analogously to high dosages (above 50 μg/day) of EE, and that even doses of NETA of 10 to 20 mg, which correspond to EE doses of approximately 20 to 30 μg/day, may in certain women be associated with increased risk. A study also found that ethinylestradiol and norethisterone had a greater influence on coagulation factors when the dose of norethisterone was 3 or 4 mg than when it was 1 mg. This might have been due to additional ethinylestradiol generated by higher doses of norethisterone.


Overdose

There have been no reports of serious
side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
s with overdose of norethisterone, even in small children.https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/016954s106lbl.pdf As such, overdose usually does not require treatment. High dosages of as much as 60 mg/day norethisterone have been studied for extended treatment durations without serious adverse effects described.


Interactions

5α-Reductase plays an important role in the
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
of norethisterone, and
5α-reductase inhibitor 5α-Reductases, also known as 3-oxo-5α-steroid 4-dehydrogenases, are enzymes involved in steroid metabolism. They participate in three metabolic pathways: bile acid biosynthesis, androgen and estrogen metabolism. There are three isozymes of ...
s such as finasteride and
dutasteride Dutasteride, sold under the brand name Avodart among others, is a medication primarily used to treat the symptoms of a benign prostatic hyperplasia (BPH), an enlarged prostate not associated with cancer. A few months may be required before benefi ...
can inhibit its metabolism. Norethisterone is partially metabolized via
hydroxylation In chemistry, hydroxylation can refer to: *(i) most commonly, hydroxylation describes a chemical process that introduces a hydroxyl group () into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of OH groups in a ...
by
CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine. It oxidizes small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from t ...
, and inhibitors and
inducer In molecular biology, an inducer is a molecule that regulates gene expression. An inducer functions in two ways; namely: *By disabling repressors. The gene is expressed because an inducer binds to the repressor. The binding of the inducer to the r ...
s of CYP3A4 can significantly alter circulating levels of norethisterone. For instance, the CYP3A4 inducers
rifampicin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), mycobacterium avium complex, ''Mycobacterium avium'' complex, leprosy, and Legionnaires’ disease. ...
and
bosentan Bosentan, sold under the brand name Tracleer and Safebo among others, is a dual endothelin receptor antagonist medication used in the treatment of pulmonary artery hypertension (PAH). Bosentan is available as film-coated tablets (62.5 mg o ...
have been found to decrease norethisterone exposure by 42% and 23%, respectively, and the CYP3A4 inducers
carbamazepine Carbamazepine (CBZ), sold under the trade name Tegretol among others, is an anticonvulsant medication used primarily in the treatment of epilepsy and neuropathic pain. It is used as an adjunctive treatment in schizophrenia along with other m ...
and
St. John's wort ''Hypericum perforatum'', known as St. John's wort, is a flowering plant in the family Hypericaceae and the type species of the genus ''Hypericum''. Possibly a hybrid between ''Hypericum maculatum, H. maculatum'' and ''Hypericum attenuatum, H. ...
have also been found to accelerate norethisterone clearance.


Pharmacology


Pharmacodynamics

Norethisterone is a potent
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. ...
and a weak
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
and
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
. That is, it is a potent
agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...
of the
progesterone receptor The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone. In humans, PR is encoded by a single ''PGR'' gene resid ...
(PR) and a weak agonist of the
androgen receptor The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor that is activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone in th ...
(AR) and the
estrogen receptor Estrogen receptors (ERs) are a group of proteins found inside cells. They are receptors that are activated by the hormone estrogen ( 17β-estradiol). Two classes of ER exist: nuclear estrogen receptors (ERα and ERβ), which are members of the ...
(ER). Norethisterone itself has insignificant
affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Par ...
for the ER; its estrogenic activity is from an
active metabolite An active metabolite is an active form of a drug after it has been processed by the body. Metabolites of drugs An active metabolite results when a drug is metabolized by the body into a modified form which continues to produce effects in the body ...
that is formed in very small amounts,
ethinylestradiol Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. In the past, EE was widely used for various indications such as the treatment of menopausal symptoms, gynecological disord ...
(EE), which is a very potent estrogen. Norethisterone and its metabolites have negligible affinity for the
glucocorticoid receptor The glucocorticoid receptor (GR, or GCR) also known as NR3C1 (nuclear receptor subfamily 3, group C, member 1) is the receptor to which cortisol and other glucocorticoids bind. The GR is expressed in almost every cell in the body and regulates ...
(GR) and
mineralocorticoid receptor The mineralocorticoid receptor (or MR, MLR, MCR), also known as the aldosterone receptor or nuclear receptor subfamily 3, group C, member 2, (NR3C2) is a protein that in humans is encoded by the ''NR3C2'' gene that is located on chromosome 4q31 ...
(MR) and hence have no
glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
,
antiglucocorticoid An antiglucocorticoid is a drug which reduces glucocorticoid activity in the body. They include direct glucocorticoid receptor antagonists such as mifepristone and synthesis inhibitors such as metyrapone, ketoconazole, and aminoglutethimide. ...
,
mineralocorticoid Mineralocorticoids are a class of corticosteroids, which in turn are a class of steroid hormones. Mineralocorticoids are produced in the adrenal cortex and influence salt and water balances (electrolyte balance and fluid balance). The primary mi ...
, or
antimineralocorticoid An antimineralocorticoid, also known as a mineralocorticoid receptor antagonist (MRA or MCRA) or aldosterone antagonist, is a diuretic drug which antagonizes the action of aldosterone at mineralocorticoid receptors. This group of drugs is ofte ...
activity.


Progestogenic activity

Norethisterone is a potent
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. ...
and binds to the PR with approximately 150% of the
affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Par ...
of
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
. In contrast, its parent compounds,
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
,
nandrolone Nandrolone, also known as 19-nortestosterone, is an androgen and anabolic steroid (AAS) which is used in the form of esters such as nandrolone decanoate (brand name Deca-Durabolin) and nandrolone phenylpropionate (brand name Durabolin). Nandrolon ...
(19-nortestosterone), and
ethisterone Ethisterone, also known as ethinyltestosterone, pregneninolone, and anhydrohydroxyprogesterone and formerly sold under the brand names Proluton C and Pranone among others, is a progestin medication which was used in the treatment of gynecologica ...
(17α-ethynyltestosterone), have 2%, 22%, and 44% of the relative binding affinity of progesterone for the PR. Unlike norethisterone, its major active metabolite 5α-dihydronorethisterone (5α-DHNET), which is formed by transformation via 5α-reductase, has been found to possess both progestogenic and marked
antiprogestogen Antiprogestogens, or antiprogestins, also known as progesterone antagonists or progesterone blockers, are a class of drugs which prevent progestogens like progesterone from mediating their biological effects in the body. They act by receptor antag ...
ic activity, although its affinity for the PR is greatly reduced relative to norethisterone at only 25% of that of progesterone. Norethisterone produces similar changes in the
endometrium The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional laye ...
and
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
, such as endometrial transformation, and is similarly antigonadotropic,
ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized ...
-inhibiting, and
thermogenic Thermogenic means tending to produce heat, and the term is commonly applied to drugs which increase heat through metabolic stimulation, or to microorganisms which create heat within organic waste. Approximately all enzymatic reaction in the huma ...
in women compared to progesterone, which is in accordance with its progestogenic activity.


Androgenic activity

Norethisterone has approximately 15% of the affinity of the
anabolic–androgenic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone as well as synthetic androgens that are structurally related and have similar effects t ...
(AAS)
metribolone Metribolone (developmental code R1881, also known as methyltrienolone) is a synthetic and orally active anabolic–androgenic steroid (AAS) and a 17α-alkylated nandrolone (19-nortestosterone) derivative which was never marketed for medical ...
(R-1881) for the AR, and in accordance, is weakly androgenic. In contrast to norethisterone, 5α-DHNET, the major metabolite of norethisterone, shows higher affinity for the AR, with approximately 27% of the affinity of metribolone. However, although 5α-DHNET has higher affinity for the AR than norethisterone, it has significantly diminished and in fact almost abolished androgenic potency in comparison to norethisterone in rodent
bioassay A bioassay is an analytical method to determine the concentration or potency of a substance by its effect on living animals or plants (''in vivo''), or on living cells or tissues(''in vitro''). A bioassay can be either quantal or quantitative, dir ...
s. Similar findings were observed for
ethisterone Ethisterone, also known as ethinyltestosterone, pregneninolone, and anhydrohydroxyprogesterone and formerly sold under the brand names Proluton C and Pranone among others, is a progestin medication which was used in the treatment of gynecologica ...
(17α-ethynyltestosterone) and its 5α-reduced metabolite, whereas 5α-reduction enhanced both the AR affinity and androgenic potency of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and
nandrolone Nandrolone, also known as 19-nortestosterone, is an androgen and anabolic steroid (AAS) which is used in the form of esters such as nandrolone decanoate (brand name Deca-Durabolin) and nandrolone phenylpropionate (brand name Durabolin). Nandrolon ...
(19-nortestosterone) in rodent bioassays. As such, it appears that the ethynyl group of norethisterone at the C17α position is responsible for its loss of androgenicity upon 5α-reduction. Norethisterone (0.5 to 3 mg/day) has been found to dose-dependently decrease circulating SHBG levels, which is a common property of androgens and is due to AR-mediated suppression of hepatic SHBG production. The drug also has estrogenic activity, and estrogens are known to increase SHBG hepatic production and circulating levels, so it would appear that the androgenic activity of norethisterone overpowers its estrogenic activity in this regard. Norethisterone is bound to a considerable extent (36%) to SHBG in circulation. Although it has lower affinity for SHBG than endogenous androgens and estrogens, Norethisterone may displace testosterone from SHBG and thereby increase free testosterone levels, and this action may contribute to its weak androgenic effects.


Estrogenic activity

Norethisterone binds to the ERs, the
ERα Estrogen receptor alpha (ERα), also known as NR3A1 (nuclear receptor subfamily 3, group A, member 1), is one of two main types of estrogen receptor, a nuclear receptor (mainly found as a chromatin-binding protein) that is activated by the sex ...
and the
ERβ Estrogen receptor beta (ERβ) also known as NR3A2 (nuclear receptor subfamily 3, group A, member 2) is one of two main types of estrogen receptor—a nuclear receptor which is activated by the sex hormone estrogen. In humans ERβ is encoded by ...
, with 0.07% and 0.01% of the
relative binding affinity In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. The etymology stems from ''ligare'', which means 'to bind'. In protein-ligand binding, the ligand is usually a mol ...
of
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development of f ...
. Due to these very low relative affinities, it is essentially inactive itself as a
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
of the ERs at clinical concentrations. However, norethisterone has been found to be a substrate for
aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many ...
and is converted in the
liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...
to a small extent (0.35%) to the highly potent estrogen
ethinylestradiol Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. In the past, EE was widely used for various indications such as the treatment of menopausal symptoms, gynecological disord ...
(EE), and for this reason, unlike most other progestins, norethisterone has some estrogenic activity. However, with typical dosages of norethisterone used in
oral contraceptive Oral contraceptives, abbreviated OCPs, also known as birth control pills, are medications taken by mouth for the purpose of birth control. Female Two types of female oral contraceptive pill, taken once per day, are widely available: * The combin ...
s (0.5 to 1 mg), the levels of EE produced are low, and it has been said that they are probably without clinical relevance. Conversely, doses of 5 and 10 mg of norethisterone, which are used in the treatment of
gynecological disorder Gynaecology or gynecology (see spelling differences) is the area of medicine that involves the treatment of women's diseases, especially those of the reproductive organs. It is often paired with the field of obstetrics, forming the combined area ...
s, are converted at rates of 0.7% and 1.0% and produce levels of EE that correspond to those produced by 30 and 60 μg dosages of EE, respectively. The levels of EE formed by 0.5 and 1 mg of norethisterone have been estimated based on higher dosages as corresponding to 2 and 10 μg dosages of EE, respectively. At high doses, norethisterone may increase the risk of
venous thromboembolism Venous thrombosis is blockage of a vein caused by a thrombus (blood clot). A common form of venous thrombosis is deep vein thrombosis (DVT), when a blood clot forms in the deep veins. If a thrombus breaks off (embolizes) and flows to the lungs to ...
due to metabolism into EE.


Neurosteroid activity

Like
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
and
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
, norethisterone is metabolized into 3,5-tetrahydro
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
s. Whether these metabolites of norethisterone interact with the GABAA receptor similarly to the 3,5-tetrahydro metabolites of progesterone and testosterone like allopregnanolone and 3α-androstanediol, respectively, is a topic that does not appear to have been studied and hence requires clarification.


Steroidogenesis inhibition

Norethisterone is a substrate for and is known to be an inhibitor of 5α-reductase, with 4.4% and 20.1% inhibition at 0.1 and 1 μM, respectively. However, therapeutic concentrations of norethisterone are in the low
nanomolar Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solut ...
range, so this action may not be clinically relevant at typical dosages. Norethisterone and its major active metabolite 5α-DHNET have been found to act as irreversible
aromatase inhibitor Aromatase inhibitors (AIs) are a class of drugs used in the treatment of breast cancer in postmenopausal women and in men, and gynecomastia in men. They may also be used off-label to reduce estrogen conversion when supplementing testosterone exog ...
s (Ki = 1.7 μM and 9.0 μM, respectively). However, like the case of 5α-reductase, the concentrations required are probably too high to be clinically relevant at typical dosages. 5α-DHNET specifically has been assessed and found to be selective in its inhibition of aromatase, and does not affect
cholesterol side-chain cleavage enzyme Cholesterol side-chain cleavage enzyme is commonly referred to as P450scc, where "scc" is an acronym for side-chain cleavage. P450scc is a mitochondrial enzyme that catalyzes conversion of cholesterol to pregnenolone. This is the first reactio ...
(P450scc), 17α-hydroxylase/ 17,20-lyase, 21-hydroxylase, or 11β-hydroxylase. Since it is not aromatized (and hence cannot be transformed into an estrogenic metabolite), unlike norethisterone, 5α-DHNET has been proposed as a potential therapeutic agent in the treatment of ER-positive
breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a re ...
.


Other activities

Norethisterone is a very weak inhibitor of
CYP2C9 Cytochrome P450 family 2 subfamily C member 9 (abbreviated CYP2C9) is an enzyme protein. The enzyme is involved in metabolism, by oxidation, of both xenobiotics, including drugs, and endogenous compounds, including fatty acids. In humans, the prote ...
and
CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine. It oxidizes small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from t ...
( IC50 = 46 μM and 51 μM, respectively), but these actions require very high concentrations of norethisterone that are far above therapeutic circulating levels (which are in the nanomolar range) and hence are probably not clinically relevant. Norethisterone and some of its 5α-reduced metabolites have been found to produce vasodilating effects in animals that are independent of sex steroid receptors and hence appear to be non-genomic in mechanism. Norethisterone stimulates the proliferation of
MCF-7 MCF-7 is a breast cancer cell line isolated in 1970 from a 69-year-old White woman. MCF-7 is the acronym of Michigan Cancer Foundation-7, referring to the institute in Detroit where the cell line was established in 1973 by Herbert Soule and co-wor ...
breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a re ...
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
s ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'', an action that is independent of the classical PRs and is instead mediated via the
progesterone receptor membrane component-1 Progesterone receptor membrane component 1 (abbreviated PGRMC1) is a protein which copurification, co-purifies with progesterone binding proteins in the liver and ovary. In humans, the PGRMC1 protein is encoded by the ''PGRMC1'' gene. The sole b ...
(PGRMC1). Certain other progestins act similarly in this assay, whereas
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
acts neutrally. It is unclear if these findings may explain the different risks of breast cancer observed with progesterone and progestins in
clinical studies Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...
.


Antigonadotropic effects

Due to its progestogenic activity, norethisterone suppresses the
hypothalamic–pituitary–gonadal axis The hypothalamic–pituitary–gonadal axis (HPG axis, also known as the hypothalamic–pituitary–ovarian/testicular axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single en ...
(HPG axis) and hence has antigonadotropic effects. The estrogenic activity of norethisterone at high doses would also be expected to contribute to its antigonadotropic effects. Due to its antigonadotropic effects, norethisterone suppresses
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
al
sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects ar ...
production Production may refer to: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in the outline of industrial organization, the act of making products (goods and services) * Production as a stati ...
, inhibits
ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized ...
in women, and suppresses
spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubule ...
in men. The
ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized ...
-inhibiting dosage of both oral norethisterone and oral NETA is about 0.5 mg/day in women. However, some conflicting data exist, suggesting that higher doses might be necessary for full inhibition of ovulation. An intramuscular injection of 200 mg NETE has been found to prevent ovulation and suppress levels of
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development of f ...
,
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
,
luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...
(LH), and
follicle-stimulating hormone Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, an ...
(FSH) in women. Early studies of oral norethisterone in men employing doses of 20 to 50 mg/day observed suppression of 17-ketosteroid
excretion Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after ...
, increased
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
excretion (due to conversion into
ethinylestradiol Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. In the past, EE was widely used for various indications such as the treatment of menopausal symptoms, gynecological disord ...
), suppression of spermatogenesis,
libido Libido (; colloquial: sex drive) is a person's overall sexual drive or desire for sexual activity. Libido is influenced by biological, psychological, and social factors. Biologically, the sex hormones and associated neurotransmitters that act up ...
, and erectile function, and incidence of
gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse (1 ...
. A dosage of oral norethisterone of 25 mg/day for 3 weeks in men has been reported to suppress testosterone levels by about 70%, to 100 to 200 ng/dL, within 4 or 5 days, as well as to suppress
sperm count A semen analysis (plural: semen analyses), also called seminogram or spermiogram, evaluates certain characteristics of a male's semen and the sperm contained therein. It is done to help evaluate male fertility, whether for those seeking pregna ...
and to have no effect on libido or erectile function over this short time period. In healthy young men, NETA alone at a dose of 5 to 10 mg/day orally for 2 weeks suppressed testosterone levels from ~527 ng/dL to ~231 ng/dL (–56%). A single 200 mg intramuscular injection of NETE alone or in combination with 2 mg
estradiol valerate Estradiol valerate (EV), sold for use by mouth under the brand name Progynova and Primiwal E4 and for use by injection under the brand names Delestrogen and Progynon Depot among others, is an estrogen medication. It is used in hormone therapy fo ...
has been found to produce a rapid, strong, and sustained decrease in gonadotropin and testosterone levels for up to one month in men. Intramuscular injections of 200 mg NETE once every 3 weeks have also been found to suppress spermatogenesis in men. Similarly, a single intramuscular injection of 50 mg NETE in combination with 5 mg estradiol valerate has been found to strongly suppress testosterone levels in men. Levels of testosterone decreased from ~503 ng/dL at baseline to ~30 ng/dL at the lowest point (–94%) which occurred at day 7 post-injection.


Pharmacokinetics

The
pharmacokinetics Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...
of norethisterone have been reviewed.


Absorption

The
oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or or ...
bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
of norethisterone is between 47 and 73%, with a mean oral bioavailability of 64%.
Micronization Micronization is the process of reducing the average diameter of a solid material's particles. Traditional techniques for micronization focus on mechanical means, such as milling and grinding. Modern techniques make use of the properties of supe ...
has been found to significantly improve the oral bioavailability of norethisterone by increasing
intestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...
absorption and reducing
intestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. A single 2 mg oral dose of norethisterone has been found to result in peak circulating levels of the drug of 12 ng/mL (40 nmol/L), whereas a single 1 mg oral dose of norethisterone in combination with 2 mg estradiol resulted in peak levels of norethisterone of 8.5 ng/mL (29 nmol/L) one-hour post-administration.


Distribution

The
plasma protein binding Plasma protein binding refers to the degree to which medications attach to proteins within the blood. A drug's efficiency may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse or diffuse t ...
of norethisterone is 97%. It is bound 61% bound to
albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...
and 36% bound to SHBG.


Metabolism

Norethisterone has an
elimination half-life Biological half-life (also known as elimination half-life, pharmacologic half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration ( Cmax) to half of Cmax in the bl ...
of 5.2 to 12.8 hours, with a mean elimination half-life of 8.0 hours. The
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
of norethisterone is very similar to that of testosterone (and nandrolone) and is mainly via reduction of the Δ4
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
to 5α- and 5β-dihydronorethisterone, which is followed by the reduction of the C3 keto
group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...
to the four
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...
s of 3,5-tetrahydronorethisterone. These
transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...
s are catalyzed by 5α- and 5β-reductase and 3α- and 3β-hydroxysteroid dehydrogenase both in the
liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...
and in extrahepatic tissues such as the
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...
,
uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
,
prostate gland The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, chemically, and physio ...
,
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
, and
breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues. In females, it serves as the mammary gland, which produces and secret ...
. With the exception of 3α,5α- and 3β,5α-tetrahydronorethisterone, which have significant affinity for the ER and are estrogenic to some degree, the 3,5-tetrahydro metabolites of norethisterone are inactive in terms of affinity for sex steroid receptors (specifically, the PR, AR, and ER). A small amount of norethisterone is also converted by
aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many ...
into EE. Norethisterone is metabolized in the liver via
hydroxylation In chemistry, hydroxylation can refer to: *(i) most commonly, hydroxylation describes a chemical process that introduces a hydroxyl group () into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of OH groups in a ...
as well, mainly by
CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine. It oxidizes small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from t ...
. Some
conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...
(including
glucuronidation Glucuronidation is often involved in drug metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosid ...
and
sulfation Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...
) of norethisterone and its metabolites occurs in spite of
steric hindrance Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
by the
ethynyl group In organic chemistry, the term ethynyl designates a functional group with a double bond with 2 carbon atoms both with sp hybridisation and a triple bond(1 sigma and 2 pi bond) . It is a species similar to acetylene (or in IUPAC ethyne ) with a less ...
at C17α. The ethynyl group of norethisterone is preserved in approximately 90% of all of its metabolites. Norethisterone is used in birth control pills, opposed to progesterone itself, because it is not metabolized as rapidly as progesterone when consumed orally. When progesterone is consumed orally it is rapidly metabolized in the gastrointestinal tract and the liver, and broken down into many different metabolites. Whereas, norethisterone is not as rapidly metabolized allowing norethisterone to be present in higher quantities allowing it to more effectively compete for progesterone receptor binding sites.


Elimination

Norethisterone is eliminated 33 to 81% in
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...
and 35 to 43% in
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
.


Chemistry

Norethisterone, also known as 17α-ethynyl-19-nortestosterone or as 17α-ethynylestra-4-en-17β-ol-3-one, is a synthetic
estrane Estrane is a C18 steroid derivative, with a gonane core. ''Estrenes'' are estrane derivatives that contain a double bond, with an example being nandrolone. '' Estratrienes'' (estrins) are estrane derivatives that contain three double bonds, fo ...
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...
and a
derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. F ...
of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
. It is specifically a derivative of testosterone in which an
ethynyl group In organic chemistry, the term ethynyl designates a functional group with a double bond with 2 carbon atoms both with sp hybridisation and a triple bond(1 sigma and 2 pi bond) . It is a species similar to acetylene (or in IUPAC ethyne ) with a less ...
has been added at the C17α position and the
methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
at the C19 position has been removed; hence, it is a combined derivative of
ethisterone Ethisterone, also known as ethinyltestosterone, pregneninolone, and anhydrohydroxyprogesterone and formerly sold under the brand names Proluton C and Pranone among others, is a progestin medication which was used in the treatment of gynecologica ...
(17α-ethynyltestosterone) and
nandrolone Nandrolone, also known as 19-nortestosterone, is an androgen and anabolic steroid (AAS) which is used in the form of esters such as nandrolone decanoate (brand name Deca-Durabolin) and nandrolone phenylpropionate (brand name Durabolin). Nandrolon ...
(19-nortestosterone). These modifications result in increased
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. ...
ic activity and
oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or or ...
bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
as well as decreased
androgenic An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This incl ...
/
anabolic Anabolism () is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy, known also as an endergonic process. Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking ...
activity.


Derivatives

Norethisterone (NET) is the
parent compound In chemistry, a parent structure is the structure of an unadorned ion or molecule from which derivatives can be visualized. Parent structures underpin systematic nomenclature and facilitate classification. Fundamental parent structures have one o ...
of a large group of progestins that includes most of the progestins known as the 19-nortestosterone derivatives. This group is divided by
chemical structure A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of at ...
into the
estrane Estrane is a C18 steroid derivative, with a gonane core. ''Estrenes'' are estrane derivatives that contain a double bond, with an example being nandrolone. '' Estratrienes'' (estrins) are estrane derivatives that contain three double bonds, fo ...
s (derivatives of norethisterone) and the
gonane Gonane is a chemical compound with formula , whose molecule can be described as three molecules or entities of cyclohexane and one of cyclopentane, fused in a particular way. More specifically, the molecule can be described as that of cyclohe ...
s (18-methylgonanes or 13β-ethylestranes; derivatives of
levonorgestrel Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B One-Step among ...
) and includes the following marketed medications: ; Estranes *
Etynodiol diacetate Etynodiol diacetate, or ethynodiol diacetate, sold under the brand names Demulen and Femulen among others, is a progestin medication which is used in birth control pills. The medication is available only in combination with an estrogen. It is tak ...
(3β-hydroxy-NET 3β,17β-diacetate) *
Lynestrenol Lynestrenol, sold under the brand names Exluton and Ministat among others, is a progestin medication which is used in birth control pills and in the treatment of gynecological disorders. The medication is available both alone and in combination ...
(3-desoxy-NET) *
Norethisterone acetate Norethisterone acetate (NETA), also known as norethindrone acetate and sold under the brand name Primolut-Nor among others, is a progestin medication which is used in birth control pills, menopausal hormone therapy, and for the treatment of gyn ...
(NET 17β-acetate) *
Norethisterone enanthate Norethisterone enanthate (NETE), also known as norethindrone enanthate, is a form of hormonal birth control which is used to prevent pregnancy in women. It is used both as a form of progestogen-only injectable birth control and in combined inject ...
(17β-enanthate) *
Noretynodrel Noretynodrel, or norethynodrel, sold under the brand name Enovid among others, is a progestin medication which was previously used in birth control pills and in the treatment of gynecological disorders but is now no longer marketed. It was availa ...
5(10)-NET) *
Norgestrienone Norgestrienone, sold under the brand names Ogyline, Planor, and Miniplanor, is a progestin medication which has been used in birth control pills, sometimes in combination with ethinylestradiol. It was developed by Roussel Uclaf and has been regis ...
9,11-NET) *
Quingestanol acetate Quingestanol acetate, sold under the brand names Demovis and Pilomin among others, is a progestin medication which was used in birth control pills but is no longer marketed. It is taken by mouth. Quingestanol acetate is a progestin, or a synt ...
(NET 17β-acetate 3-cyclopentyl enol ether) *
Tibolone Tibolone, sold under the brand name Livial among others, is a medication which is used in menopausal hormone therapy and in the treatment of postmenopausal osteoporosis and endometriosis. The medication is available alone and is not formulated ...
(7α-methyl-δ5(10)-NET) ; Gonanes *
Desogestrel Desogestrel is a progestin medication which is used in birth control pills for women. It is also used in the treatment of menopausal symptoms in women. The medication is available and used alone or in combination with an estrogen. It is taken ...
(3-deketo-11-methylene-18-methyl-NET) *
Etonogestrel Etonogestrel is a medication which is used as a means of birth control for women. It is available as an implant placed under the skin of the upper arm under the brand names Nexplanon and Implanon, and in combination with ethinylestradiol, an e ...
(11-methylene-18-methyl-NET) *
Gestodene Gestodene, sold under the brand names Femodene and Minulet among others, is a progestin medication which is used in birth control pills for women. It is also used in menopausal hormone therapy. The medication is available almost exclusively in ...
(18-methyl-δ15-NET) *
Gestrinone Gestrinone, sold under the brand names Dimetrose and Nemestran among others, is a medication which is used in the treatment of endometriosis. It has also been used to treat other conditions such as uterine fibroids and heavy menstrual bleeding a ...
(18-methyl-δ9,11-NET) *
Levonorgestrel Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B One-Step among ...
(18-methyl-NET) * Norelgestromin (18-methyl-NET 3-oxime) *
Norgestimate Norgestimate, sold under the brand names Ortho Tri-Cyclen and Previfem among others, is a progestin medication which is used in birth control pills for women and in menopausal hormone therapy. The medication is available in combination with an ...
(18-methyl-NET 3-oxime 17β-acetate) *
Norgestrel Norgestrel, sold under the brand name Ovral among others, is a progestin medication which is used in birth control pills and in menopausal hormone therapy. It is available both in combination with an estrogen and alone. It is taken by mouth. S ...
(13-ethyl-NET) Several of these act as
prodrug A prodrug is a medication or compound that, after intake, is metabolized (i.e., converted within the body) into a pharmacologically active drug. Instead of administering a drug directly, a corresponding prodrug can be used to improve how the drug ...
s of norethisterone, including NETA, NETE,
etynodiol diacetate Etynodiol diacetate, or ethynodiol diacetate, sold under the brand names Demulen and Femulen among others, is a progestin medication which is used in birth control pills. The medication is available only in combination with an estrogen. It is tak ...
,
lynestrenol Lynestrenol, sold under the brand names Exluton and Ministat among others, is a progestin medication which is used in birth control pills and in the treatment of gynecological disorders. The medication is available both alone and in combination ...
, and
quingestanol acetate Quingestanol acetate, sold under the brand names Demovis and Pilomin among others, is a progestin medication which was used in birth control pills but is no longer marketed. It is taken by mouth. Quingestanol acetate is a progestin, or a synt ...
.
Noretynodrel Noretynodrel, or norethynodrel, sold under the brand name Enovid among others, is a progestin medication which was previously used in birth control pills and in the treatment of gynecological disorders but is now no longer marketed. It was availa ...
may also be a prodrug of norethisterone. NETA is taken by mouth similarly to norethisterone, while NETE is given by injection into muscle.


Non-17α-ethynylated

19-Nortestosterone (19-NT) progestins which are technically not derivatives of norethisterone (as they do not have a C17α
ethynyl group In organic chemistry, the term ethynyl designates a functional group with a double bond with 2 carbon atoms both with sp hybridisation and a triple bond(1 sigma and 2 pi bond) . It is a species similar to acetylene (or in IUPAC ethyne ) with a less ...
) but are still closely related (with other substitutions at the C17α and/or C16β positions) include the following marketed medications: * The C17α
vinyl Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from vinyl m ...
(ethenyl) derivatives
norgesterone Norgesterone, also known as norvinodrel or vinylestrenolone and sold under the brand name Vestalin, is a progestin medication which was formerly used in birth control pills for women but is now no longer marketed. It was used in combination with ...
(17α-vinyl-δ5(10)-19-NT) and
norvinisterone Norvinisterone, sold under the brand names Neoprogestin and Nor-Progestelea, is a progestin and androgen/ anabolic steroid (AAS) medication which was used in Europe but is now no longer marketed. It is taken by mouth. Norvinisterone is a proge ...
(17α-vinyl-19-NT) * The C17α
allyl In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, ...
derivatives
allylestrenol Allylestrenol, sold under the brand names Gestanin and Turinal among others, is a progestin medication which is used to treat recurrent and threatened miscarriage and to prevent premature labor in pregnant women. However, except in the case of p ...
(3-deketo-17α-allyl-19-NT) and
altrenogest Altrenogest, sold under the brand names Swinemate and Altren manufactured by Aurora Pharmaceutical and Regumate manufactured by Merck, is a progestin of the 19-nortestosterone group which is widely used in veterinary medicine to suppress or sync ...
(17α-allyl-δ9,11-19-NT) * The C17α
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...
derivative
normethandrone Normethandrone, also known as methylestrenolone or methylnortestosterone and sold under the brand name Metalutin among others, is a progestin and androgen/anabolic steroid (AAS) medication which is used in combination with an estrogen in the tre ...
(17α-methyl-19-NT) * The C17α cyanomethyl derivative
dienogest Dienogest, sold under the brand name Visanne among others, is a progestin medication which is used in birth control pills and in the treatment of endometriosis. It is also used in menopausal hormone therapy and to treat heavy periods. Dienogest ...
(17α-cyanomethyl-δ9-19-NT) * The C16β ethyl derivative
oxendolone Oxendolone, sold under the brand names Prostetin and Roxenone, is an antiandrogen and progestin medication which is used in Japan in the treatment of enlarged prostate. However, this use is controversial due to concerns about its clinical effic ...
(16β-ethyl-19-NT) Many
anabolic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone (medication), testosterone as well as synthetic androgens that are structurally related ...
s of the 19-nortestosterone family, like
norethandrolone Norethandrolone, sold under the brand names Nilevar and Pronabol among others, is an androgen and anabolic steroid (AAS) medication which has been used to promote muscle growth and to treat severe burns, physical trauma, and aplastic anemia but h ...
and
ethylestrenol Ethylestrenol, also known as ethyloestrenol or ethylnandrol and sold under the brand names Maxibolin and Orabolin among others, is an androgen and anabolic steroid (AAS) medication which has been used in the past for a variety of indications such ...
, are also potent progestogens, but were never marketed as such.


Synthesis

Chemical syntheses of norethisterone have been published.


Synthesis 1

Estradiol 3-methyl ether (1, EME) is partially reduced to the 1,5-diene (2) as also occurs for the first step in the synthesis of nandrolone.
Oppenauer oxidation Oppenauer oxidation, named after , is a gentle method for selectively oxidizing secondary alcohols to ketones. The reaction is the opposite Meerwein–Ponndorf–Verley reduction. The alcohol is oxidized with aluminium isopropoxide in excess ...
then transforms the C17β hydroxyl group into a ketone functionality (3). This is then reacted with metal
acetylide In organometallic chemistry, acetylide refers to chemical compounds with the chemical formulas and , where M is a metal. The term is used loosely and can refer to substituted acetylides having the general structure (where R is an organic side c ...
into the corresponding C17α
ethynyl In organic chemistry, the term ethynyl designates a functional group with a double bond with 2 carbon atoms both with sp hybridisation and a triple bond(1 sigma and 2 pi bond) . It is a species similar to acetylene (or in IUPAC ethyne ) with a less ...
compound (4). Hydrolysis of the enol ether under mild conditions leads directly to (5), which appears to be
noretynodrel Noretynodrel, or norethynodrel, sold under the brand name Enovid among others, is a progestin medication which was previously used in birth control pills and in the treatment of gynecological disorders but is now no longer marketed. It was availa ...
(although Lednicer states that it is "etynodrel" in his book (which may be a synonym etynodiol); etynodrel is with a
chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
atom attached), an orally active progestin. This is the progestogen component of the first
oral contraceptive Oral contraceptives, abbreviated OCPs, also known as birth control pills, are medications taken by mouth for the purpose of birth control. Female Two types of female oral contraceptive pill, taken once per day, are widely available: * The combin ...
to be offered for sale (i.e., Enovid). Treatment of the ethynyl enol ether with strong acid leads to norethisterone (6). In practice, these and all other combined oral contraceptives are mixtures of 1 to 2% EE or mestranol and an oral
progestin A progestogen, also referred to as a progestagen, gestagen, or gestogen, is a type of medication which produces effects similar to those of the natural product, natural female sex hormone progesterone in the body. A progestin is a ''synthetic co ...
. It has been speculated that the discovery of the necessity of estrogen in addition to progestin for contraceptive efficacy is due to the presence of a small amount of unreduced EME (1) in early batches of 2. This when subjected to oxidation and ethynylation, would of course lead to mestranol (3). In any event, the need for the presence of estrogen in the mixture is now well established experimentally.


Synthesis 2

Norethisterone is made from estr-4-ene-3,17-dione (bolandione), which in turn is synthesized by partial reduction of the aromatic region of the 3-O-methyl ether of
estrone Estrone (E1), also spelled oestrone, is a steroid, a weak estrogen, and a minor female sex hormone. It is one of three major endogenous estrogens, the others being estradiol and estriol. Estrone, as well as the other estrogens, are synthesized ...
with lithium in liquid ammonia, and simultaneously of the keto group at C17α to a hydroxyl group, which is then oxidized back to a keto group by
chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple ...
in
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
. The conjugated C4-C5 olefin and the carbonyl group at C3 is then transformed to dienol ethyl ether using ethyl orthoformate. The obtained product is ethynylated by
acetylene Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
in the presence of
potassium tert-butoxide Potassium ''tert''-butoxide is the chemical compound with the formula K+(CH3)3CO−. This colourless solid is a strong base (pKa of conjugate acid around 17), which is useful in organic synthesis. It exists as a tetrameric cubane-type cluster ...
. After
hydrochloride In chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (e.g. an amine). An alternative name is chlorhydrate, which comes from French. An archaic alternative n ...
hydrolysis of the formed O-potassium derivative, during which the enol ether is also hydrolyzed, and the remaining double bond is shifted, the desired norethisterone is obtained.


History

Norethisterone was synthesized for the first time by chemists Luis Miramontes,
Carl Djerassi Carl Djerassi (October 29, 1923 – January 30, 2015) was an Austrian-born Bulgarian-American pharmaceutical chemist, novelist, playwright and co-founder of Djerassi Resident Artists Program with Diane Middlebrook, Diane Wood Middlebrook. He is b ...
, and
George Rosenkranz George Rosenkranz (born György Rosenkranz; 20 August 1916 – 23 June 2019) was a pioneering Mexican scientist in the field of steroid chemistry, who used native Mexican plant sources as raw materials. He was born in Hungary, studied in Switzerl ...
at Syntex in
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
in 1951. It was
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
from
ethisterone Ethisterone, also known as ethinyltestosterone, pregneninolone, and anhydrohydroxyprogesterone and formerly sold under the brand names Proluton C and Pranone among others, is a progestin medication which was used in the treatment of gynecologica ...
, and was found to possess about 20-fold greater potency as a progestogen in comparison. Norethisterone was the first highly active oral
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. ...
to be synthesized, and was preceded (as a progestogen) by
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
(1934), ethisterone (1938), 19-norprogesterone (1944), and 17α-methylprogesterone (1949) as well as by
nandrolone Nandrolone, also known as 19-nortestosterone, is an androgen and anabolic steroid (AAS) which is used in the form of esters such as nandrolone decanoate (brand name Deca-Durabolin) and nandrolone phenylpropionate (brand name Durabolin). Nandrolon ...
(1950), whereas
noretynodrel Noretynodrel, or norethynodrel, sold under the brand name Enovid among others, is a progestin medication which was previously used in birth control pills and in the treatment of gynecological disorders but is now no longer marketed. It was availa ...
(1952) and
norethandrolone Norethandrolone, sold under the brand names Nilevar and Pronabol among others, is an androgen and anabolic steroid (AAS) medication which has been used to promote muscle growth and to treat severe burns, physical trauma, and aplastic anemia but h ...
(1953) followed the synthesis of norethisterone. The drug was introduced as ''Norlutin'' in the United States in 1957. Norethisterone was subsequently combined with mestranol and marketed as ''Ortho-Novum'' in the United States in 1963. It was the second progestin, after
noretynodrel Noretynodrel, or norethynodrel, sold under the brand name Enovid among others, is a progestin medication which was previously used in birth control pills and in the treatment of gynecological disorders but is now no longer marketed. It was availa ...
in 1960, to be used in an
oral contraceptive Oral contraceptives, abbreviated OCPs, also known as birth control pills, are medications taken by mouth for the purpose of birth control. Female Two types of female oral contraceptive pill, taken once per day, are widely available: * The combin ...
. In 1964, additional contraceptive preparations containing norethisterone in combination with mestranol or EE, such as ''Norlestrin'' and ''Norinyl'', were marketed in the United States.


Society and culture


Generic names

''Norethisterone'' is the and of the drug while ''norethindrone'' is its .


Brand names

Norethisterone (NET), including as NETA and NETE, has been marketed under many brand names throughout the world.


Availability


United States

Norethisterone was previously available alone in 5 mg tablets under the brand names Norlutin in the United States, but this formulation has since been discontinued in this country. However, NETA remains available alone in 5 mg tablets under the brand name Aygestin in the United States. It is one of the only non-contraceptive progestogen-only drug formulations that remains available in the United States. The others include
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...
,
medroxyprogesterone acetate Medroxyprogesterone acetate (MPA), also known as depot medroxyprogesterone acetate (DMPA) in injectable form and sold under the brand name Depo-Provera among others, is a hormonal medication of the progestin type. It is used as a method of bi ...
,
megestrol acetate Megestrol acetate (MGA), sold under the brand name Megace among others, is a progestin medication which is used mainly as an appetite stimulant to treat wasting syndromes such as cachexia.https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/ ...
, and
hydroxyprogesterone caproate Hydroxyprogesterone caproate (OHPC), sold under the brand names Proluton and Makena among others, is a progestin medication which is used to prevent preterm birth in pregnant women with a history of the condition and to treat gynecological dis ...
, as well as the atypical agent
danazol Danazol, sold as Danocrine and other brand names, is a medication used in the treatment of endometriosis, fibrocystic breast disease, hereditary angioedema and other conditions. It is taken by mouth. The use of danazol is limited by masculini ...
. Both norethisterone and NETA are also available in the United States as contraceptives. Norethisterone is available both alone (brand names Camila, Errin, Heather, Micronor, Nor-QD, others) and in combination with EE (Norinyl, Ortho-Novum, others) or mestranol (Norinyl, Ortho-Novum, others), while NETA is available only in combination with EE (Norlestrin, others). NETE is not available in the United States in any form.


Research

Norethisterone, as NETA and NETE, has been studied for use as a potential male hormonal contraceptive in combination with
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
in men. Long-acting norethisterone microspheres for
intramuscular injection Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles have ...
have been studied for potential use in birth control.


References


Further reading

* * * * * * * * * * * *


External links

* {{Portal bar, Medicine Ethynyl compounds 3β-Hydroxysteroid dehydrogenase inhibitors 5α-Reductase inhibitors Alkene derivatives Androgens and anabolic steroids Aromatase inhibitors Enones Estranes Hormonal contraception Human drug metabolites Progestogens Syntex Synthetic estrogens