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 biochemi ...

, partial agonists are drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a

full 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 ag ...

. They may also be considered ligands 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 ag ...

and antagonistic 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 rec ...

, 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 Buspirone, sold under the brand name Buspar, among others, is a medication primarily used to treat anxiety disorders, particularly generalized anxiety disorder. Benefits support its short-term use. It is taken by mouth, and it may take up to fo ...

aripiprazole Aripiprazole, sold under the brand names Abilify and Aristada among others, is an atypical antipsychotic. It is primarily used in the treatment of schizophrenia and bipolar disorder. Other uses include as an add-on treatment in major depress ...

buprenorphine Buprenorphine is an opioid used to treat opioid use disorder, acute pain, and chronic pain. It can be used under the tongue (sublingual), in the cheek (buccal), by injection (intravenous and subcutaneous), as a skin patch (transdermal ...

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 Peroxisome proliferator- activated receptor gamma (PPAR-γ or PPARG), also known as the glitazone reverse insulin resistance receptor, or NR1C3 (nuclear receptor subfamily 1, group C, member 3) is a type II nuclear receptor functioning as a tran ...

as partial agonists are

honokiol Honokiol is a lignan isolated from the bark, seed cones, and leaves of trees belonging to the genus ''Magnolia''. It has been identified as one of the chemical compounds in some traditional eastern herbal medicines along with magnolol, 4-O-methy ...

and

falcarindiol Falcarindiol is a polyyne found in carrot roots which has antifungal activity. Falcarindiol is the main compound responsible for bitterness in carrots. Falcarindiol and other falcarindiol-type polyacetylenes are also found in many other plants ...

. Delta 9-tetrahydrocannabivarin ( THCV) is a partial agonist at CB2 receptors and this activity might be implicated in ∆9-THCV-mediated

anti-inflammatory Anti-inflammatory is the property of a substance or treatment that reduces inflammation or swelling. Anti-inflammatory drugs, also called anti-inflammatories, make up about half of analgesics. These drugs remedy pain by reducing inflammation as ...

effects. Additionally, Delta-9-Tetrahydrocannabinol (

THC Tetrahydrocannabinol (THC) is the principal psychoactive constituent of cannabis and one of at least 113 total cannabinoids identified on the plant. Although the chemical formula for THC (C21H30O2) describes multiple isomers, the term ''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