In the field of pharmacology, potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug (e.g., fentanyl, alprazolam, risperidone) evokes a larger response at low concentrations, while a drug of lower potency (codiene, diazepam, ziprasidone) evokes a small response at low concentrations. It is proportional to affinity and efficacy.