The EC50 of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed.[2] The EC50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response,[3] after a specified exposure duration.
It is also related to IC50 which is a measure of a compound's inhibition (50% inhibition). For competition binding assays and functional antagonist assays IC50 is the most common summary measure of the dose-response curve. For agonist/stimulator assays the most common summary measure is the EC50.[4]