Which statement describes a partial agonist?

• A. Produces a submaximal response even at full receptor occupancy.
• B. Produces a maximal response equal to full agonist.
• C. Has no efficacy.
• D. Binds irreversibly to receptor.

Answer: (A)

Partial agonists have lower intrinsic efficacy than full agonists. Even when every receptor is occupied, they cannot trigger the full signaling needed for a maximal response, so the effect remains submaximal. This is why the statement that a partial agonist produces a submaximal response even at full receptor occupancy is the best description. The other ideas describe different concepts: a maximal response equal to the full agonist would define a full agonist; having no efficacy describes an antagonist with zero efficacy; and binding irreversibly refers to binding kinetics, which doesn’t define partial agonism on its own.