Antagonist
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A substance that counteracts the effects of another agent.
Pharmacologically, an antagonist interacts with a receptor to inhibit the action of agents (agonists) that produce specific physiological or behavioral effects mediated by that receptor.
See also: agonist.Reference: World Health Organization. Lexicon of alcohol and drug terms published by the World Health Organization. Internet. Accessed August 20, 2009. Available at http://www.who.int/substance_abuse/terminology/who_lexicon/en/index.html
