A receptor antagonist is any given ligand that binds to a receptor in some way without causing any immediate or downstream response, essentially neutralizing the receptor until something with a stronger affinity removes the antagonist or the antagonist itself unbinds. Generally, antagonists can act one of two ways: 1) they can either block the receptors directly, preventing the usual ligand from binding, such as in the case of atropine when it blocks specific acetylcholine receptors to provide important medical benefits. This is competitive antagonism, as they are competing for the same binding sites on the receptor. The other is by binding to a receptor in a site other than the designated receptor site, inducing a conformational change to prevent the usual ligand(s) from binding and activating a downstream cascade. A commonly-seen and used receptor antagonist is naloxone, another opioid competitive antagonist typically used to treat opioid overdoses by blocking receptors outright. Further elaboration can be found in "Orthosteric v. Allosteric Modulators."