What type of antagonist binds to a receptor's active site?

The competitive antagonist is a type of antagonist that binds to the active site of a receptor. By occupying the same binding site as the endogenous ligand or agonist, the competitive antagonist effectively prevents the agonist from binding and activating the receptor. This interaction is reversible, and increasing the concentration of the agonist can overcome the effects of the competitive antagonist, restoring the receptor’s activity.

The essence of a competitive antagonist's action lies in its ability to directly compete with the agonist for binding to the active site. This characteristic is distinct from non-competitive antagonists and allosteric antagonists, which bind to different sites and do not directly block the agonist’s access to the active site. Non-competitive antagonists, for example, may bind to an allosteric site, altering the receptor's shape or function without competing for the active site, while allosteric antagonists similarly affect the receptor's activity but from a different binding location, rather than directly blocking the agonist's access.

In summary, the competitive antagonist's primary mechanism of action is its binding to the receptor's active site, thereby inhibiting agonist action through direct competition.