Definition
An antagonist binds a receptor but does not activate it, preventing agonists from producing their effect. Competitive antagonists occupy the same site as the agonist, so their blockade can be overcome by higher agonist concentrations, shifting the concentration–response curve to the right without lowering its maximum. Non-competitive antagonists bind elsewhere or irreversibly and reduce the maximal response. Inverse agonists go further, suppressing a receptor's constitutive activity. Antagonists are essential research tools, because blocking a response with a selective antagonist helps confirm which receptor mediates it. Peptide examples include exendin(9–39) at the GLP-1 receptor and degarelix at the GnRH receptor, the latter an approved prescription medicine.