Definition
EC50 is the concentration of an agonist that produces half of its maximal effect in a specific assay. It is obtained by fitting a sigmoidal concentration–response curve, usually plotted on a logarithmic concentration axis, with a four-parameter logistic model. A lower EC50 indicates higher potency. The related IC50 is the concentration producing 50% inhibition. EC50 values are assay-dependent: receptor expression level, signalling readout, incubation time and cell background all shift them, so values are comparable only within the same system. Potency is also distinct from efficacy, the maximal response, and from binding affinity. Many incretin analogues are characterised by EC50 values for cAMP production at each target receptor.