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".
^MILES AA, PERRY EL. Biological potency and its relation to therapeutic efficacy. Bull World Health Organ. 1953;9(1):1-14. PMID: 13082386; PMCID: PMC2542104.