The following pharmacological definition has been taken from the Pharmacology and Experimental Therapeutics Department Glossary at Boston University School of Medicine .
The joint effect of two or more drugs such that the combined effect is less than the sum of the effects produced by each agent separately. The agonist is the agent producing the effect that is diminished by the administration of the antagonist. Antagonisms may be any of three general types:
caused by combination of agonist with antagonist, with resulting inactivation of the agonist, e.g., dimercaprol and mercuric ion.
caused by agonist and antagonist acting at two independent sites and inducing independent, but opposite effects.
caused by action of the agonist and antagonist at the same site.
In the case of pharmacological antagonisms, the terms competitive and non-competitive antagonism are used with meanings analogous to competitive and non-competitive enzyme inhibition as used in enzymology. (See Symposium on Drug Antagonism, Pharm. Rev. 9: 211, 1952).
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