Agonist: Difference between revisions

An '''agonist''' is a chemical that binds to the [[receptor]] of a cell and activates the receptor to cause a physiological response. An agonist initiates the same reaction typically produced by the binding of an endogenous ligand (such as a hormone or neurotransmitter) with a receptor.<ref>Agonist definition (Merriam-Webster) http://www.merriam-webster.com/dictionary/agonist</ref> A drug’s ability to affect a given receptor is dependent on the drug’s affinity and intrinsic efficacy towards that receptor. The affinity of a drug describes the strength of attraction between it and a given receptor, and consequently its ability to bind to that receptor. A drug with a high affinity for a receptor has a high likelihood of binding to it, while a drug with a low affinity has a lesser degree of attraction towards a receptor.  

This contrasts the efficacy of a drug, which describes a drug's capacity to produce a response when bound to a receptor. A drug with high efficacy will produce a proportionally stronger effect than a drug of lower efficacy occupying the same number of receptors. The maximum efficacy of a drug reflects the greatest attainable response to a particular drug on a receptor set regardless of dose. A drug with a high efficacy may need to occupy fewer receptors to produce maximum effects, meaning it will not produce stronger effects beyond a certain dosage.   

In contrast to an agonist, an [[antagonist]] is a chemical that binds to the receptor of a cell without causing a physiological response. Receptor antagonists work by blocking or diminishing the effects produced by endogenous or drug-induced agonism of a receptor.  

[[Category:Neuroscience]]