From a dose–response curve, which parameter denotes potency?

• A. EC50, the dose producing 50% of the maximal effect.
• B. NOAEL
• C. LOAEL
• D. LC50

Answer: (A)

Potency on a dose–response curve is determined by the dose required to achieve a given level of effect. The standard measure is EC50—the dose (or concentration) that produces 50% of the maximal response. A smaller EC50 means the drug is more potent because less is needed to reach half of the maximum effect.

Efficacy, by contrast, refers to the maximum effect a drug can produce (Emax). Two drugs can have the same efficacy but different potencies if they have different EC50 values. The other terms are about safety or toxicity, not potency: NOAEL and LOAEL mark doses at which no adverse effect or adverse effects first appear, respectively, and LC50 is the lethal concentration for 50% of a population.