When I use a word . . . Medical definitions: adverse events, effects, and reactions

Abstract

An adverse event in a medical context is any abnormal sign, symptom, laboratory test, syndromic combination of such abnormalities, untoward or unplanned occurrence (e.g. an accident or unplanned pregnancy), or unexpected deterioration in a concurrent illness. Such events may or may not be associated with the use of a medicinal product. An adverse drug reaction is an appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product, usually predicting hazard from future administration and warranting prevention, or specific treatment, or alteration of the dosage regimen, or withdrawal of the product. Adverse reactions manifest as symptoms or signs that affected individuals themselves recognise. An adverse drug effect, which differs from an adverse drug reaction, is a potentially harmful effect resulting from an intervention related to the use of a medicinal product, which constitutes a hazard and may or may not be associated with a clinically appreciable adverse reaction and/or an abnormal laboratory test or clinical investigation, as a marker of an adverse reaction. Adverse effects do not themselves manifest as symptoms or signs but, as the definition states, can be detected by laboratory tests or clinical investigations. Certain terms in this area should be avoided, particularly “idiosyncrasy,” which should be replaced by a statement about the nature of an individual’s susceptibility, “well tolerated,” which often prematurely presumes an absence of adverse effects, and “toxicities,” which unjustifiably pluralises a non-count noun and is used colloquially to mean adverse effects and reactions in general. The term “side effect” is better restricted to colloquial use and not used in technical texts.

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