The graph below shows a dose-response curve for two drugs, Drug A and Drug B. Based on the graph, which drug is MORE POTENT?

Correct answer: D. Drug B

• A. Drug A reaches a higher maximum effect (greater efficacy), but it requires a HIGHER concentration to achieve 50% of its maximum effect. Higher concentration requirement = lower potency. Drug A is MORE EFFICACIOUS (higher Emax) but LESS POTENT than Drug B.
• B. The two drugs are NOT equally potent. Drug B's EC50 is at a lower concentration than Drug A's, making Drug B more potent.
• C. The graph clearly shows that Drug B achieves its 50% maximum effect at a lower concentration than Drug A, which is sufficient to determine that Drug B is more potent.
• D. CORRECT. Potency refers to the concentration of a drug required to produce 50% of its maximum effect (EC50). Drug B reaches 50% of its maximum effect at a LOWER concentration than Drug A (its curve is shifted to the LEFT on the x-axis). A drug that achieves the same effect at a lower dose is MORE POTENT. Drug B is more potent (though it may have lower efficacy/Emax than Drug A).