How can the effect of a competitive antagonist be reversed?

• A. By increasing the concentration of the agonist.
• B. By increasing the antagonist concentration.
• C. By lowering the temperature.
• D. By removing the agonist.

Answer: (A)

Competitive antagonists bind reversibly to the same receptor site as the agonist, blocking activation. Because their binding is reversible and they compete for the same site, increasing the concentration of the agonist can outcompete the antagonist. As more receptors are occupied by the agonist, signaling is restored and, with enough agonist, the maximal response can be reached again. This is the hallmark of surmountable competitive antagonism: you can overcome the blockade by simply raising the agonist level.

Increasing antagonist concentration would worsen the block; lowering the temperature doesn’t reliably overcome competition; removing the agonist stops signaling but doesn’t address the competitive blockade.