any effect of a drug, chemical, or other medicine that is in addition to its intended effect, especially an effect that is harmful or unpleasant.
any accompanying or consequential and usually detrimental effect: the side effects of air pollution.
Affect vs. Effect: Use The Correct Word Every TimeWhen do you use AFFECT vs EFFECT? Use this easy rule to always know when to use affect vs effect.
Origin of side effect
First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for side effect
any unwanted nontherapeutic effect caused by a drugCompare aftereffect (def. 2)
any secondary effect, esp an undesirable one
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Medicine definitions for side effect
A peripheral or secondary effect, especially an undesirable secondary effect of a drug or therapeutic regimen.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.