Which term describes the ability of a drug to produce its maximum therapeutic effect?

• A. Potency
• B. Efficacy
• C. Safety
• D. Toxicity

Answer: (B)

The concept tested here is the maximal effect a drug can produce, which is its efficacy. Efficacy describes the height of the drug’s response on a dose–response curve—the ultimate ceiling of therapeutic effect, independent of how much you dose. A drug can be highly potent (requiring a small amount to reach a given effect) yet have limited efficacy if it cannot produce a strong, full response; conversely, a drug with high efficacy can achieve a strong maximal effect even if it needs a larger dose to start producing that effect, though potency and dose requirements are separate concepts. Safety and toxicity relate to adverse effects and harm, not the ability to achieve the maximum therapeutic effect. For example, a full agonist can reach the maximum possible response, demonstrating high efficacy, whereas a partial agonist cannot reach that same maximum, reflecting lower efficacy.