Antagonist (pharmacology)

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Competitive and non- competitive inhibition of the effect of an agonist . A parallel right shift of the concentration-effect curve of an agonist by a competitive antagonist is characteristic, while noncompetitive antagonists usually lead to a reduction in the maximum effect .

An antagonist (from ancient Greek ἀνταγωνιστής antagōnistēs , German 'rival, enemy [in war, in court]' ) is a substance in pharmacology that inhibits an agonist in its action without itself triggering a pharmaceutically significant effect. Corresponding agonists can be hormones or neurotransmitters , for example . Active ingredients that increase the effect of another are called synergists .

Types of antagonists

According to their mode of action, antagonists are differentiated based on their competitiveness :

Inverse agonists and allosteric modulators are sometimes also referred to as antagonists . In addition to their partial agonistic action, partial agonists also have an antagonistic active component, that is to say they can inhibit the action of a full agonist.


The potency of an antagonist can be given as the antagonist concentration, for example in the form of the mean inhibitory concentration ( IC 50 ), which leads to a half-maximal inhibition of the effect triggered by an agonist, or more characteristically with the help of the Schild plot as the pA 2 value . The affinity of an antagonist for the receptor (pK i or pK B ) is also a good measure of its potency.

See also

  • Inhibitor : an inhibitor that influences one or more reactions in such a way that they are slowed down, inhibited or prevented


  • Klaus Aktories, Ulrich Förstermann and others: General and special pharmacology and toxicology. 10th edition, Urban & Fischer, 2009, ISBN 3-437-42522-6 , pp. 8-13. limited preview in Google Book search

Individual evidence

  1. ^ Wilhelm Pape , Max Sengebusch (arrangement): Concise dictionary of the Greek language . 3rd edition, 6th impression. Vieweg & Sohn, Braunschweig 1914 ( [accessed December 5, 2019]).

Web links

Wiktionary: Antagonist  - explanations of meanings, word origins, synonyms, translations