Emax represents which aspect of drug effect?

• A. The EC50 value.
• B. The dose required for 50% effect.
• C. The maximal response produced by the drug.
• D. The duration of action.

Answer: (C)

Emax is the maximal response a drug can produce under optimal conditions; it defines the drug’s efficacy. This value sits at the top of the dose–response curve, showing how large a full effect the drug can achieve regardless of further dose increases. The EC50 (or ED50) measures potency—the amount of drug needed to reach half of that maximal effect—not how big the effect can be. The duration of action is about how long the effect lasts, not its magnitude. So the maximum achievable response—the plateau of the curve—best describes Emax.