Which term describes a compound able to elicit a maximal response from receptors?

• A. Full agonist
• B. Partial agonist
• C. Inverse agonist
• D. Physiological antagonist

Answer: (A)

Maximal receptor response is determined by efficacy. A full agonist binds to the receptor and drives it into the active conformation with high intrinsic efficacy, capable of triggering the system’s maximal response. In other words, it can produce the greatest possible effect when it fully engages the receptors. Sometimes this max effect can be reached even without occupying every receptor if there are spare receptors that amplify signaling, but the key point is that a full agonist has enough efficacy to generate the maximum response. By contrast, a partial agonist has lower efficacy and cannot reach the same maximal effect even at high occupancy, an inverse agonist reduces the receptor’s baseline activity, and a physiological antagonist blocks activation without producing a response itself.