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.
Quick GuideWomen's Health: Nutrition and Health Care Reform
Subscribe to MedicineNet's Women's Health Newsletter
Women's Health Resources
Last Editorial Review: 5/13/2016