A result of drug or other therapy in addition to or in extension of the desired therapeutic effect; usually but not necessarily, connoting an undesirable effect. Although technically the therapeutic effect carried beyond the desired limit ( e.g., a hemorrhage from an anticoagulant) is a s., the term more often refers to pharmacologic results of therapy unrelated to the usual objective ( e.g., a development of signs of Cushing syndrome with steroid therapy).
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side effect n a secondary and usu. adverse effect (as of a drug) <toxic side effects> <a side effect of drowsiness caused by antihistamines> called also side reaction
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a consequence other than the one(s) for which an agent or measure is used, as the adverse effects produced by a drug, especially on a tissue or organ system other than the one sought to be benefited by its administration.Medical dictionary. 2011.