Potency

Potency is a functional-pharmacology measure describing the concentration of a ligand required to produce a specified magnitude of response — usually half of the maximum response the system can generate. For agonists this is reported as the EC50; for inhibitors and antagonists it is reported as the IC50.

Potency reflects a combination of affinity and efficacy and is system-dependent: the same ligand can display different EC50 values in different cell types depending on receptor density and coupling efficiency. Comparisons of potency between compounds are therefore meaningful only within a single, defined assay system.