Published December 01, 2023 by

Agonist vs Antagonist || Classifications, Differences, Mechanism of Action


Agonists are types of drug that bind and activate a receptor and induces many physiological reactions. They can make physiological responses in the body and turn the neurotransmitters in action.

Agonists type with examples 

01. Full agonist 

E.g: heroin, methadone, morphine, opium

02. Partial agonist

E.g: buspirone, buprenorphine, narclozapine

03. Orthosteric agonist

E.g: imatinib

04. Direct agonist

E.g: morphine, nicotine 

05. Indirect agonist

E.g: cocaine 

06. Inverse agonist

E.g: GABAA, mu opoid, histamine

07. Physiological agonist

E.g: epinephrine & hepatocyte growth factor(HGF)

08. Endogenous agonist

E.g: serotonin for serotonin receptors & dopamine for dopamine receptors

09. Exogenous agonist

E.g: heroin, caffeine, ibuprofen 

10. Selective agonist

E.g: buspirone is a selective agonist for serotonin 5-HT1A. 


Antagonists are the type of drug that limits/ inhibits the action of agonists. They exert their pharmacological effects by playing the opposing role of the agonists. They works by blocking the activation of certain receptors of cell and by preventing biological responses.

Types of Antagonists with example 

1. Full antagonist 

E.g: naltrexone & naloxone

2. Chemical antagonist 

E.g: narcan, naltrexone

3. Physiological antagonist 

E.g: glucagon

4. Pharmacokinetic antagonist 

E.g: phenobarbital 

5. Allosteric antagonist 

E.g: barbiturates & benzodiazepines

6. Negative allosteric antagonist 

E.g: flumazenil, bicuculline, gabazine

7. Competitive antagonist 

E.g: naloxone

8. Non-competitive antagonist 

E.g: ketamine

9. Partial antagonist 

E.g: adrenargic blockers

10. Mixed antagonist 

E.g: pentazocine, butorphanol, buprenorphine

      Agonist vs Antagonist
Drug that activates a receptorDrug that does not activate a receptor
Does not interfere with the action of antagonistsPrevent the activation of the receptor by an agonist
Differ in both afficacy & affinity for the receptor Are zero efficacy drugs
Agonists compete with other agonist for binding siteCompetitive antagonists bind to the same receptor
Produces an action or responseProduces It's opposition response
Initiates the action of neurotransmitters in the brainBlocks the action of neurotransmitters
After binding with receptors, agonists initiate physiological response Blocks or inhibits physiological responses after binding with receptors
Types include full agonist, inverse agonist, direct agonist, indirect agonist etc.Types are: full antagonist, physical antagonist, chemical antagonist, competitive antagonist, non-competitive antagonist etc.

General Mechanism of Action of Agonist

General Mechanism of Action of Antagonist