Drugreceptor

A drug receptor is a biomolecule that binds to a drug and initiates a cellular response. Most receptors are proteins expressed on the cell surface or within the cell, including cytosolic and nuclear receptors. Binding of a drug to its receptor alters the receptor's conformation and triggers signaling pathways, enzyme activity changes, or gene transcription, leading to a physiological effect.

Receptors are highly specific for their ligands and show varying affinity and selectivity. The relationship between receptor occupancy and effect can be described by potency (the dose or concentration required for a given effect) and efficacy (the maximal effect achievable). Early models used the occupancy theory, but modern pharmacology recognizes that efficacy and intrinsic activity determine the response even with partial occupancy.

Receptors are grouped into major families: cell-surface receptors such as G protein-coupled receptors (GPCRs), ligand-gated ion channels, and enzyme-linked receptors; and intracellular receptors that regulate gene transcription (for example, steroid hormone receptors).

Drugs can be classified by how they interact: agonists activate receptors; antagonists bind without activating; inverse agonists reduce constitutive receptor activity; partial agonists produce submaximal responses.

Chronic exposure to drugs can alter receptor function or number, a process called desensitization or downregulation; upregulation can occur in some circumstances. These adaptations influence tolerance and withdrawal.

Understanding receptors guides drug development and therapy, enabling selectivity to minimize side effects. Examples include beta-adrenergic receptors targeted by beta-blockers, mu-opioid receptors targeted by opioids, and GABA-A receptors targeted by benzodiazepines.