A drug that irreversibly binds to an allosteric site is best described as which?

• A. Competitive antagonist.
• B. Noncompetitive antagonist.
• C. Partial agonist.
• D. Noncompetitive agonist.

Answer: (B)

Binding at an allosteric site changes receptor function in a way that isn’t overcome by adding more agonist. If the antagonist binds irreversibly, the receptor can’t respond fully to the endogenous ligand, so the maximal effect is reduced and the effect persists. This is the hallmark of noncompetitive antagonism.

In contrast, a competitive antagonist sits at the active site and can be outcompeted by high concentrations of the agonist, so efficacy can still be reached with enough agonist. A partial agonist produces a smaller maximal response even when it occupies receptors. A noncompetitive agonist isn’t the standard descriptor here.