Which statement about potency and ED50 is correct?

Which statement about potency and ED50 is correct?

• A. A larger ED50 indicates higher potency.
• B. A smaller ED50 indicates higher potency.
• C. Potency is independent of ED50.
• D. Potency is determined solely by the rate of onset.

Answer: (B)

Potency is determined by how much drug is needed to produce a given level of effect. The ED50 is the dose that produces 50% of the maximal response. If you need a smaller dose to reach half-maximal effect, the drug is more potent; if you need a larger dose, it is less potent. This relationship is illustrated on the dose–response curve as a shift to the left for higher potency (lower ED50) and to the right for lower potency (higher ED50). The rate of onset reflects pharmacokinetics and how quickly effects begin, but it does not define potency. Hence, a smaller ED50 indicates higher potency.

Potency is determined by how much drug is needed to produce a given level of effect. The ED50 is the dose that produces 50% of the maximal response. If you need a smaller dose to reach half-maximal effect, the drug is more potent; if you need a larger dose, it is less potent. This relationship is illustrated on the dose–response curve as a shift to the left for higher potency (lower ED50) and to the right for lower potency (higher ED50). The rate of onset reflects pharmacokinetics and how quickly effects begin, but it does not define potency. Hence, a smaller ED50 indicates higher potency.