FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam 2025 - Free NABP Practice Questions and Study Guide

A competitive antagonist works by binding to the same receptor site as an agonist but does not activate the receptor. This blocks the agonist from binding and exerting its effects. As a result, the presence of a competitive antagonist primarily alters the potency of the agonist, which refers to the amount of agonist required to achieve a certain effect.

When a competitive antagonist is present, a higher concentration of the agonist is needed to overcome the antagonist's binding and elicit a response. This means that while the agonist may still be effective if provided in sufficient quantities, the effective dose will be increased, which directly relates to its potency.

Understanding this interaction is crucial in pharmacology, as it emphasizes how competitive antagonists can modulate the effects of agonists in therapeutic and clinical settings. The other options do not accurately characterize the role of a competitive antagonist in this context. Reducing efficacy pertains to intrinsic activity at the receptor, which isn't affected in the same manner. Enhancing absorption and increasing toxicity do not directly relate to the pharmacodynamic interactions between an agonist and a competitive antagonist.