potency (pharmacology) potency (pharmacology) 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 given response at low concentrations, while a drug of lower potency (meperidine, ziprasidone, furosemide) evokes the same response only at higher concentrations. higher potency does not necessarily mean greater effectiveness or more side effects. concentration-response curves illustrating the concept of potency. for a response of 0.25a.u., drug b is more potent, as it generates this response at a lower concentration. for a response of 0.75a.u., drug a is more potent. a.u. refers to "arbitrary units". the iuphar has stated that 'potency' is "an imprecise term that should always be further defined", for instance as ec 50 , ic 50 , ed 50 , ld 50 and so on.