An agonist and an antagonist can both bind the same receptor with equal affinity. What distinguishes them, and why does that make an antagonist useful as a treatment for overdose?

C. Binding is not the same as activating: one triggers, one just occupies.

The receptor binds and activates, and the distinction lives entirely in the second, an antagonist is a key that enters the lock and will not turn, and while it sits there nothing else gets in. Which explains a clinical detail: naloxone wears off faster than many opioids, so a revived patient can relapse. The reversal is a displacement, not a cure.