Short definitions of the receptor pharmacology terms used across The Agonists. For fuller explanations, follow the links in our articles. Educational information only, not medical advice.
How strongly a molecule binds to its receptor. Often expressed as a dissociation constant (Kd or Ki); a lower value means tighter binding.
A molecule that binds to a receptor and activates it, producing a response.
A molecule that binds to a site on the receptor separate from the main (orthosteric) site and changes how the receptor responds to its agonist.
A molecule that binds to a receptor without activating it, blocking or reducing the effect of agonists.
A protein that binds activated G protein-coupled receptors, switching off G protein signalling and helping move receptors into the cell; it can also start signals of its own.
When an agonist favours one of a receptor's signalling pathways over another, compared with a reference agonist. Also called functional selectivity.
Antagonism in which the antagonist competes with the agonist for the same binding site; it can be overcome by more agonist.
Activity a receptor shows without any agonist bound. Inverse agonists reduce it.
A fall in a receptor's response during continued or repeated exposure to an agonist.
A graph of the size of a drug's effect against its dose or concentration, usually plotted on a log scale.
The concentration of a drug that produces half of its own maximal effect; a common measure of potency.
The ability of a drug, once bound, to activate its receptor and produce a response. It sets the maximum effect (Emax).
The maximal response a drug can produce in a given system.
A messenger made by the body itself, such as adrenaline, acetylcholine, dopamine or endorphins.
An agonist that can produce the maximal response the system allows.
A receptor with seven membrane-spanning helices that signals through G proteins; the largest family of drug targets.
A molecule that reduces a receptor's activity below its resting (constitutive) level.
Any molecule that binds to a receptor, whether agonist, antagonist or modulator.
A receptor that is itself an ion channel and opens when an agonist binds, such as nicotinic acetylcholine and GABA-A receptors.
An intracellular receptor that, when activated, changes gene expression; examples include steroid and thyroid hormone receptors.
The receptor's main binding site, where the natural messenger binds.
An agonist that produces less than the maximal response even when all receptors are occupied.
The amount of drug needed to produce a given effect. A more potent drug needs a lower concentration.
A protein that recognises a specific chemical signal and changes cell activity in response.
A situation in which a maximal response is reached with only a fraction of receptors occupied (also called spare receptors).
A drug's preference for one receptor or subtype over others. It is relative and decreases at higher concentrations.
The ratio between the dose causing harm and the dose producing the desired effect; a narrow index means a small margin.
A reduced response to a drug after repeated use, so that the same amount has less effect.
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