Receptor pharmacology

Receptor pharmacology is the study of how molecules bind to receptor proteins on or inside cells and how that binding changes cell activity.

A receptor is a protein shaped to recognize particular molecules, called ligands, and to respond by altering a signal inside the cell. The core concepts are affinity, how tightly a ligand binds, and efficacy, how strongly it activates the receptor once bound. Agonists activate a receptor, partial agonists activate it incompletely, antagonists bind without activating and block other ligands, inverse agonists reduce a receptor's baseline activity, and allosteric modulators bind at a second site and adjust the receptor's response to its main ligand.

Most cannabinoid receptors, including CB1 and CB2, belong to the family of G protein-coupled receptors, which relay signals through proteins inside the membrane. THC is a partial agonist at CB1, which accounts for its intoxicating effects, while CBD has low affinity for CB1 and CB2 and instead acts as a negative allosteric modulator at CB1 and interacts with serotonin, TRP and other targets. These profiles are measured in laboratory binding and functional assays and explain differences between cannabinoids before any clinical effect is considered.