Intrinsic activity is best described as

• A. The rate of metabolism
• B. The ability of a drug to generate an effect
• C. The drug's color
• D. The rate of excretion

Answer: (B)

Intrinsic activity is about how effectively a drug, once bound to its receptor, can produce a response. It reflects efficacy, not how tightly the drug binds (affinity) or how much is needed to get an effect (potency). A drug with high intrinsic activity can elicit a large maximum effect when it occupies receptors (a full agonist), while one with lower intrinsic activity yields a smaller maximum effect even at full occupancy (a partial agonist). Antagonists bind without activating the receptor, so they have little to no intrinsic activity, and some drugs can even reduce baseline activity (inverse agonists) depending on the system. The other options describe pharmacokinetic properties like metabolism or excretion, or irrelevant traits like color.