On a dose-response curve, two drugs A and B produce the same maximum effect, but Drug A reaches 50% of the maximum effect (EC50) at a lower concentration than Drug B. Which drug is MORE POTENT?

Correct answer: D. Drug A

• A. When both drugs reach the same maximum effect, potency CAN be compared using EC50. The drug with the lower EC50 is more potent.
• B. Drug B requires a HIGHER concentration to reach EC50, meaning it is LESS potent than Drug A.
• C. The drugs are equally efficacious (same maximum effect) but NOT equally potent — Drug A is more potent.
• D. CORRECT. Potency refers to the concentration (or dose) required to produce a given effect. A more potent drug achieves the same effect at a LOWER concentration. Drug A reaches EC50 at a lower concentration than Drug B, making Drug A more potent. Potency does NOT equal efficacy — both drugs reach the same maximum effect (equal efficacy).