EC50

EC50 — the half-maximal effective concentration — is the concentration of an agonist that produces a response equal to half of that agonist's own maximum response in a defined assay system. It is derived from a fitted concentration-response curve, most commonly a four-parameter logistic (Hill) equation.

EC50 is a measure of potency, not affinity: it reflects both how well the ligand binds and how efficiently the resulting receptor conformation drives the measured downstream signal in that particular assay. Comparisons of EC50 across different assay platforms should therefore be made with caution.