pharmacology Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...

, partial agonists are drugs that bind to and activate a given

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

, but have only partial

efficacy Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as ''effectiveness'', and it has often been used synonymously, although in pharmacology a pragmatic clinical trial#Efficacy versu ...

at the receptor relative to a full agonist. They may also be considered

ligands 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 electro ...

which display both

agonistic 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 agoni ...

and

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

ic effects—when both a full agonist and partial agonist are present, the partial agonist actually acts as a

competitive antagonist A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of recep ...

, competing with the full agonist for receptor occupancy and producing a net decrease in the receptor activation observed with the full agonist alone. Clinically, partial agonists can be used to activate receptors to give a desired submaximal response when inadequate amounts of the endogenous ligand are present, or they can reduce the overstimulation of receptors when excess amounts of the endogenous ligand are present. Some currently common drugs that have been classed as partial agonists at particular receptors include buspirone, aripiprazole, buprenorphine,

nalmefene Nalmefene is an opioid antagonist medication used in the management of opioid overdose and alcohol dependence. It is taken by mouth. Nalmefene is an opiate derivative similar in both structure and activity to the opioid antagonist naltrexone. ...

and

norclozapine ''N''-Desmethylclozapine (NDMC), or norclozapine, is a major active metabolite of the atypical antipsychotic drug clozapine. Unlike clozapine, it possesses intrinsic activity at the D2/ D3 receptors, and acts as a weak partial agonist at these ...

. Examples of ligands activating peroxisome proliferator-activated receptor gamma as partial agonists are honokiol and falcarindiol. Delta 9-tetrahydrocannabivarin (

THCV Tetrahydrocannabivarin (THCV, THV, O-4394, GWP42004) is a homologue of tetrahydrocannabinol (THC) having a propyl (3-carbon) side chain instead of a pentyl (5-carbon) group on the molecule, which makes it produce very different effects from THC. ...

) is a partial agonist at CB2 receptors and this activity might be implicated in ∆9-THCV-mediated anti-inflammatory effects. Additionally, Delta-9-Tetrahydrocannabinol ( THC) is a partial agonist at both the CB1 and CB2 receptors, with the former being responsible for its psychoactive effects.

References

Pharmacodynamics {{pharmacology-stub

See also

References