What must antagonists have regarding their action?

• A. Bind effectively, but have significant intrinsic activity
• B. Bind weakly, with high intrinsic activity
• C. Bind effectively and have some intrinsic activity
• D. Bind effectively, but have little or no intrinsic activity

Answer: (D)

Antagonists work by occupying receptors without activating them, so they can block the effect of an agonist. To do this effectively, they must bind with high affinity to the receptor, ensuring they outcompete the endogenous ligand. At the same time, they should have little or no intrinsic activity, meaning they do not produce a receptor response on their own. If an antagonist had significant intrinsic activity, it would elicit some effect (or act like a partial/biased agonist), undermining its ability to block the agonist. So the combination of strong binding and minimal functional activity best fits how antagonists operate.