Antagonist

An antagonist can be a drug or chemical that binds to a molecular receptor and blocks or otherwise antagonizes the ability of natural agonists to themselves bind and/or interact with the receptor. Antagonists may block receptors in a number of ways, including binding to and physically blocking a receptor's active site or binding to other separate, unique sites that may regulate a receptor's activity. Depending on the antagonist and receptor involved, the antagonist activity at a receptor may be reversible or irreversible. Regardless, different antagonists will bind with different receptors with different affinities.