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Definition of Adverse reaction

Adverse reaction: In pharmacology, any unexpected or dangerous reaction to a drug. An unwanted effect caused by the administration of a drug. The onset of the adverse reaction may be sudden or develop over time.

Also called an adverse drug event (ADE), adverse drug reaction (ADR), adverse effect or adverse event.

Source: MedTerms™ Medical Dictionary
http://www.medterms.com/script/main/art.asp?articlekey=26227
Last Editorial Review: 8/14/2004

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