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.
Many people undergoing chemotherapy experience a frustrating side effect often called "chemo brain."
From Science Daily • Jun. 10, 2026
It’s one more side effect of the booming market for artificial intelligence.
From Barron's • Jun. 1, 2026
But even people who don’t mean to hurt capybaras can still do harm to them, an unfortunate side effect of them living in such proximity to humans.
From Slate • May 27, 2026
Popular weight loss drugs may have a surprising side effect: stalling cancer.
From The Wall Street Journal • May 22, 2026
It wasn't the point of the paper chain, but it was a great side effect.
From "Linked" by Gordon Korman
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.
