Which statement best distinguishes potency from efficacy?

Which statement best distinguishes potency from efficacy?

• A. Potency equals the maximal effect; efficacy is the dose needed for effect
• B. Potency relates to the amount of drug needed for an effect; efficacy relates to the maximal effect
• C. Potency and efficacy are identical
• D. Potency relates to duration; efficacy relates to onset

Answer: (B)

Potency and efficacy describe two different aspects of how a drug acts. Potency is about the amount of drug needed to produce a given effect—the more potent a drug, the smaller the dose required. Efficacy is about the maximal effect a drug can produce, regardless of the dose used. So the statement that potency relates to the amount of drug needed for an effect and efficacy relates to the maximal effect is the correct distinction. The other options mix up these ideas: potency isn’t the maximal effect, efficacy isn’t about the dose, they’re not identical, and duration/onset aren’t what define potency or efficacy.

Potency and efficacy describe two different aspects of how a drug acts. Potency is about the amount of drug needed to produce a given effect—the more potent a drug, the smaller the dose required. Efficacy is about the maximal effect a drug can produce, regardless of the dose used. So the statement that potency relates to the amount of drug needed for an effect and efficacy relates to the maximal effect is the correct distinction. The other options mix up these ideas: potency isn’t the maximal effect, efficacy isn’t about the dose, they’re not identical, and duration/onset aren’t what define potency or efficacy.