Noncompetitive antagonist refers to two distinct phenomena: one in which the antagonist binds to the active site of the receptor, and one in which the antagonist binds to an allosteric site of the receptor. Unlike competitive antagonists, which affect the amount of agonist necessary to achieve a maximal response but do not affect the magnitude of that maximal response, non-competitive antagonists reduce the magnitude of the maximum response that can be attained by any amount of agonist. This property earns them the name "non-competitive" because their effects cannot be negated, no matter how much agonist is present. Cyclothiazide has been shown to act as a reversible non-competitive antagonist of mGluR1
