Which type of drug blocks receptor activity with little intrinsic activity?

• A. Agonist
• B. Antagonist
• C. Partial agonist
• D. Inverse agonist

Answer: (B)

Blocking receptor activity with little intrinsic activity means the drug binds without activating the receptor, preventing other agonists from producing a response. That is the defining property of an antagonist. It sits on the receptor and doesn't generate a signal on its own, so it can blunt or prevent effects that would be produced by full or partial agonists. In contrast, a full agonist activates the receptor to produce a maximal response; a partial agonist has limited intrinsic activity and yields a partial response; an inverse agonist reduces baseline receptor activity by having negative intrinsic activity. Antagonists can be competitive or noncompetitive, shifting the dose–response relationship without providing their own signaling.