In toxicology, the median lethal dose, LD50 (abbreviation for "lethal
dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a measure of
the lethal dose of a toxin, radiation, or pathogen. The value of LD50
for a substance is the dose required to kill half the members of a
tested population after a specified test duration. LD50 figures are
frequently used as a general indicator of a substance's acute
toxicity. A lower LD50 is indicative of increased toxicity.
The test was created by J.W. Trevan in 1927. The term semilethal
dose is occasionally used with the same meaning, in particular in
translations from non-English-language texts, but can also refer to a
sublethal dose; because of this ambiguity, it is usually avoided. LD50
is usually determined by tests on animals such as laboratory mice. In
2011, the U.S.
Food and Drug Administration
Food and Drug Administration approved alternative
methods to LD50 for testing the cosmetic drug
Botox without animal
Animal rights concerns
5 See also
5.1 Other measures of toxicity
5.2 Related measures
7 External links
The LD50 is usually expressed as the mass of substance administered
per unit mass of test subject, typically as milligrams of substance
per kilogram of body mass, sometimes also stated as nanograms
(suitable for botulinum), micrograms, or grams (suitable for
paracetamol) per kilogram. Stating it this way allows the relative
toxicity of different substances to be compared, and normalizes for
the variation in the size of the animals exposed (although toxicity
does not always scale simply with body mass). For substances in the
environment, such as poisonous vapors or substances in water that are
toxic to fish, the concentration in the environment (per cubic metre
or per litre) is used, giving a value of LC50. But in this case, the
exposure time is important (see below).
The choice of 50% lethality as a benchmark avoids the potential for
ambiguity of making measurements in the extremes and reduces the
amount of testing required. However, this also means that LD50 is not
the lethal dose for all subjects; some may be killed by much less,
while others survive doses far higher than the LD50. Measures such as
"LD1" and "LD99" (dosage required to kill 1% or 99%, respectively, of
the test population) are occasionally used for specific purposes.
Lethal dosage often varies depending on the method of administration;
for instance, many substances are less toxic when administered orally
than when intravenously administered. For this reason, LD50 figures
are often qualified with the mode of administration, e.g., "LD50 i.v."
The related quantities LD50/30 or LD50/60 are used to refer to a dose
that without treatment will be lethal to 50% of the population within
(respectively) 30 or 60 days. These measures are used more commonly
Radiation Health Physics, as survival beyond 60 days usually
results in recovery.
A comparable measurement is LCt50, which relates to lethal dosage from
exposure, where C is concentration and t is time. It is often
expressed in terms of mg-min/m3. ICt50 is the dose that will cause
incapacitation rather than death. These measures are commonly used to
indicate the comparative efficacy of chemical warfare agents, and
dosages are typically qualified by rates of breathing (e.g., resting =
10 l/min) for inhalation, or degree of clothing for skin
penetration. The concept of Ct was first proposed by
Fritz Haber and
is sometimes referred to as Haber's Law, which assumes that exposure
to 1 minute of 100 mg/m3 is equivalent to 10 minutes of
10 mg/m3 (1 × 100 = 100, as does 10 × 10 = 100).
Some chemicals, such as hydrogen cyanide, are rapidly detoxified by
the human body, and do not follow Haber's Law. So, in these cases, the
lethal concentration may be given simply as LC50 and qualified by a
duration of exposure (e.g., 10 minutes). The Material Safety Data
Sheets for toxic substances frequently use this form of the term even
if the substance does follow Haber's Law.
For disease-causing organisms, there is also a measure known as the
median infective dose and dosage. The median infective dose (ID50) is
the number of organisms received by a person or test animal qualified
by the route of administration (e.g., 1,200 org/man per oral). Because
of the difficulties in counting actual organisms in a dose, infective
doses may be expressed in terms of biological assay, such as the
number of LD50's to some test animal. In biological warfare infective
dosage is the number of infective doses per cubic metre of air times
the number of minutes of exposure (e.g., ICt50 is 100 medium doses -
As a measure of toxicity, LD50 is somewhat unreliable and results may
vary greatly between testing facilities due to factors such as the
genetic characteristics of the sample population, animal species
tested, environmental factors and mode of administration.
There can be wide variability between species as well; what is
relatively safe for rats may very well be extremely toxic for humans
(cf. paracetamol toxicity), and vice versa. For example, chocolate,
comparatively harmless to humans, is known to be toxic to many
animals. When used to test venom from venomous creatures, such as
snakes, LD50 results may be misleading due to the physiological
differences between mice, rats, and humans. Many venomous snakes are
specialized predators on mice, and their venom may be adapted
specifically to incapacitate mice; and mongooses may be exceptionally
resistant. While most mammals have a very similar physiology, LD50
results may or may not have equal bearing upon every mammal species,
such as humans, etc.
Note: Comparing substances (especially drugs) to each other by LD50
can be misleading in many cases due (in part) to differences in
effective dose (ED50). Therefore, it is more useful to compare such
substances by therapeutic index, which is simply the ratio of LD50 to
The following examples are listed in reference to LD50 values, in
descending order, and accompanied by LC50 values, bracketed , when
LD50 : g/kg
LC50 : g/L
Sucrose (table sugar)
Glucose (blood sugar)
Monosodium glutamate (MSG)
Stevioside (from stevia)
mice & rats, oral
Vitamin C (ascorbic acid)
Lactose (milk sugar)
Ethanol (Grain alcohol)
Sodium isopropyl methylphosphonic acid (IMPA, metabolite of sarin)
Fructose (fruit sugar)
Sodium chloride (table salt)
Delta-9-tetrahydrocannabinol (THC) + Polysorbate 80
rat, oral
Alkyl dimethyl benzalkonium chloride (ADBAC)
aquatic invertebrates, immersion
Coumarin (benzopyrone, from
Cinnamomum aromaticum and other plants)
Psilocybin (from magic mushrooms)
Aspirin (acetylsalicylic acid)
Methylenedioxymethamphetamine (MDMA, ecstasy)
Uranyl acetate dihydrate
7002114000000000000♠114 mg/kg (estimated)
Thiopental sodium (used in lethal injection)
Vitamin D3 (cholecalciferol)
Piperidine (from black pepper)
Lysergic acid diethylamide
Lysergic acid diethylamide (LSD)
6.5–13.0 mg/kg (estimated)
Chlorotoxin (CTX, from scorpions)
1–2 mg/kg (estimated)
Cantharidin (from blister beetles)
Aflatoxin B1 (from Aspergillus flavus mold)
Amatoxin (from Amanita phalloides mushrooms)
Tetrodotoxin (TTX, from blue-ringed octopus)
mouse, subcutaneous injection
Robustoxin (from Sydney funnel-web spider)
human, oral, inhalation, absorption through skin/eyes
6999140000000000000♠140 µg/kg (estimated)
Venom of the Brazilian wandering spider
Venom of the
Inland Taipan (Australian snake)
Ricin (from castor oil plant)
2,3,7,8-Tetrachlorodibenzodioxin (TCDD, in Agent Orange)
CrTX-A (from box jellyfish venom)
Latrotoxin (from widow spider venom)
Batrachotoxin (from poison dart frog)
human, sub-cutaneous injection
6997200000000000000♠2–7 µg/kg (estimated)
Abrin (from rosary pea)
Maitotoxin (from ciguateric fish)
6995100000000000000♠10 ng/kg (estimated)
Shiga toxin (from dysentery)
Tetanospasmin (tetanus toxin)
Botulinum toxin (Botox)
human, oral, injection, inhalation
6994100000000000000♠1 ng/kg (estimated)
Animal rights concerns
Animal-rights and animal-welfare groups, such as Animal Rights
International, have campaigned against LD50 testing on animals.
Several countries, including the UK, have taken steps to ban the oral
LD50, and the Organisation for Economic Co-operation and Development
(OECD) abolished the requirement for the oral test in 2001 (see Test
Guideline 401, Trends in Pharmacological Sciences Vol 22, February 22,
Other measures of toxicity
Certain safety factor
Fixed Dose Procedure to estimate LD50
Median toxic dose (TD50)
Lowest published toxic concentration (TCLo)
Lowest published lethal dose (LDLo)
EC50 (half maximal effective concentration)
IC50 (half maximal inhibitory concentration)
Indicative limit value
No-observed-adverse-effect level (NOAEL)
Lowest-observed-adverse-effect level (LOAEL)
TCID50 Tissue Culture Infective Dosage
EID50 Egg Infective Dosage
ELD50 Egg Lethal Dosage
Plaque forming units (pfu)
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Concepts in pharmacology
Volume of distribution (Initial)
Rate of infusion
Onset of action
Mean residence time
Plasma protein binding
Therapeutic index (Median lethal dose, Effective dose)
Mechanism of action
Dose–response relationship (Efficacy, Potency)
Antimicrobial pharmacodynamics: Minimum inhibitory concentration
Minimum bactericidal concentration (Bactericide)
Agonist: Inverse agonist
Antagonist: Competitive antagonist
Drug tolerance: Tachyphylaxis
Drug resistance: Antibiotic resistance
Multiple drug resistance
Neuropsychopharmacology (Neuropharmacology, Psychopharmacology)
History of poison
In vitro toxicology
Acceptable daily intake
Fixed Dose Procedure
Whole bowel irrigation
1858 Bradford sweets poisoning
2007 pet food recalls
Niigata Minamata disease
Poisoning of Alexander Litvinenko
Consumption of Tide Pods
List of poisonings
List of extremely hazardous substances
Occupational safety and health