If two drugs produce the same maximal effect, which statement is true?

If two drugs produce the same maximal effect, which statement is true?

• A. They have equal potency and equal efficacy
• B. The drug with higher ED50 has greater efficacy
• C. They have equal efficacy; the one with lower ED50 is more potent
• D. Potency cannot be inferred from ED50

Answer: (C)

When two drugs reach the same maximal effect, they have equal efficacy. Potency, on the other hand, is about the dose needed to produce a given effect. The ED50 is the dose that yields 50% of the maximal effect, so the drug that achieves that level at a lower dose is more potent. Therefore, they have equal efficacy; the one with the lower ED50 is more potent. If one drug has a higher ED50, it is less potent, not more potent or more efficacious. ED50 provides a direct measure of potency, so potency can be inferred from ED50.

When two drugs reach the same maximal effect, they have equal efficacy. Potency, on the other hand, is about the dose needed to produce a given effect. The ED50 is the dose that yields 50% of the maximal effect, so the drug that achieves that level at a lower dose is more potent. Therefore, they have equal efficacy; the one with the lower ED50 is more potent. If one drug has a higher ED50, it is less potent, not more potent or more efficacious. ED50 provides a direct measure of potency, so potency can be inferred from ED50.