In chemistry, antagonism is a phenomenon wherein two or more agents in combination have an overall effect that is less than the sum of their individual effects.
The word is most commonly used in this context in biochemistry and toxicology: interference in the physiological action of a chemical substance by another having a similar structure. For instance, a receptor antagonist is an agent that reduces the response that a ligand produces when the receptor antagonist binds to a receptor on a cell. An example of this is the interleukin-1 receptor antagonist. The opposite of antagonism is synergy. It is a negative type of synergism.
^Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation: Synergistic and antagonistic effects. M. N. Peyrat-Maillard, M. E. Cuvelier and C. Berset, Journal Of The American Oil Chemists' Society, 2003, Volume 80, Number 10, pages 1007-1012, doi:10.1007/s11746-003-0812-z