What does a drug acting as a competitive antagonist do?

A drug that acts as a competitive antagonist binds to the same receptor as an agonist but does not activate it. Instead, it competes with the agonist for binding to the receptor site, effectively inhibiting the action of the agonist. This interaction leads to a decrease in the receptor's activation, thus reducing or blocking the physiological response that would typically occur if the agonist were present.

In contrast, a competitive antagonist does not enhance the effect of the agonist, nor does it activate the cellular response. It directly opposes the action of the agonist by preventing it from eliciting its intended effects. Therefore, the primary role of a competitive antagonist is to inhibit the action of the agonist. Additionally, it is not correct to say that a competitive antagonist has no effect on the receptor; its very purpose is to interfere with the receptor's normal function by blocking the agonist's access.