Agonists, Antagonists (competitive and noncompetitive), Spare receptors, Addiction, Tolerance, Dependence, Tachyphylaxis, Idiosyncrasy, Allergy : Pharmaguideline -->

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Agonists, Antagonists (competitive and noncompetitive), Spare receptors, Addiction, Tolerance, Dependence, Tachyphylaxis, Idiosyncrasy, Allergy

They bind to and activate a receptor, producing the maximum possible response that an agonist may elicit at the receptor.


It attaches to a receptor and activates it, resulting in a biological reaction Endogenous agonist (such as hormones or neurotransmitters) and external agonists can both activate receptors (like drugs).

Agonists are classified into the following sub-categories:

Agonists in their entirety

They bind to and activate a receptor, producing the maximum possible response that an agonist may elicit at the receptor.


A co-agonist collaborates with other co-agonists to achieve the intended effect.

Agonists that are selective

A selective agonist is solely active on a single kind of receptor.

Participant agonists

Partial agonists, such as buprinorpine, bind and activate a particular receptor but have just a fraction of the efficiency of a complete agonist at the receptor, even when the receptor is fully occupied.

Opposite agonists

Receptor inverse agonists bind to the same receptor binding sites as agonists and make the receptor less active. have the opposite pharmacological action of an agonist

Agonists with superpowers

It is a word used to describe a chemical that can elicit a higher response than natural agonists for the target receptor.

Agonists that are irreversible

An irreversible agonist is a kind of agonist that forms covalent connections with a receptor and binds to it forever.


Competitive agonist

An antagonist binds to the same binding site on the receptor as agonists or ligands but doesn't act on it.

Antibodies and agonists both try to attach to the same receptor. When a sufficient quantity of antagonist is present, the agonist is displaced from the binding sites, resulting in less frequent receptor activation. The relative affinity of each molecule for the site, as well as their individual concentrations, defines the degree of receptor activation. Competitive antagonists are used to inhibiting drug action and to counteract the effects of previously ingested medications.

Non-competitive agonist

Non-competitive antagonists operate in one of two ways: they either link to the receptor's active area or bind to an allosteric location. It is referred to as an allosteric antagonist if it binds to the allosteric site. End results in both scenarios are functionally equivalent. Non-competitive antagonists diminish the size of the maximum response that may be reached by any quantity of agonists, as opposed to competitive antagonists, which influence the number of agonists required to achieve a maximal response but not the amplitude of that peak response.

Spare receptors

Spare receptors are those receptors that can produce the greatest response without combining.


Addiction is a brain condition characterized by obsessive participation in rewarding stimuli in the face of negative consequences. It is linked to both rewarding and reinforcing addictive behavior.


Tolerance is described as "the declining action of a medicine caused by repeated administration at a given dose." Substance tolerance is a pharmacological term that describes a subject's diminished responsiveness to a drug after repeated usage.

When the biological reaction to a chemical is diminished as a result of frequent usage, pharmacodynamic tolerance develops. Pharmacokinetic tolerance arises as a result of a reduced amount of the substance reaching the site of action, which may be induced by an increase in the induction of enzymes necessary for drug breakdown.


It is characterized as "an adaptive condition linked with a withdrawal syndrome following the termination of repetitive exposure to a stimulus (e.g., drug ingestion)."


Tachyphylaxis is a subcategory of drug tolerance that refers to situations of abrupt, short-term tolerance following medication delivery. It is a short-term and quick development of drug tolerance. It can happen after a single large dosage or after a succession of lesser ones.


Idiosyncratic medication responses occur seldom and unexpectedly in the general population. They typically arise as a result of new medication exposure. They are classified as an uncommon ADR. They don't appear to be concentration sensitive.


The first time a person is exposed to a drug, an allergic reaction will not develop. The initial encounter permits the body to produce antibodies and memory lymphocyte cells in response to the antigen. Following that, antibodies or lymphocytes engage with the antigen, resulting in allergic responses.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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