side effect
Americannoun
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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.
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any accompanying or consequential and usually detrimental effect.
the side effects of air pollution.
noun
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any unwanted nontherapeutic effect caused by a drug Compare aftereffect
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any secondary effect, esp an undesirable one
Etymology
Origin of side effect
First recorded in 1880–85
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
But there’s also a quieter side effect I’ve come to love.
From Salon • May 12, 2026
What will the next scan bring when it comes to a treatment, surgery, or side effect that means this healthy, happy moment was fleeting?
From Slate • May 6, 2026
More recently, it’s become an off-label success story after doctors realized a side effect of taking the drug was hair growth.
From MarketWatch • Apr. 27, 2026
But scientists are now raising concerns about an unexpected side effect.
From Science Daily • Apr. 18, 2026
“It’s okay. I think it’s a side effect from... you know, your time in the Underworld. Hopefully it’ll get easier.”
From "The Son of Neptune" by Rick Riordan
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
