side effect

noun

: a secondary and usually adverse effect (as of a drug)
toxic side effects

called also side reaction

Examples of side effect in a Sentence

Nausea and diarrhea are the side effects of the drug. the harmful side effects of using chemicals to kill insects The merger created positive side effects for both companies.
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Sonu matched or outperformed conventional treatments, with no reported side effects. Tanya Benedicto Klich, Forbes.com, 27 June 2025 Any burden on adults is, according to the ruling, merely a side effect of this legitimate regulation. Meg Leta Jones, The Conversation, 27 June 2025 Thirteen-year-old Mei is a boy-band-crazy girl whose puberty has a fascinating side effect: her mood swings turn her into a giant red panda. Barry Levitt, Time, 26 June 2025 The drug had similar side effects to Wegovy despite delivering more weight loss. Annika Kim Constantino,ashley Capoot, CNBC, 25 June 2025 See All Example Sentences for side effect

Word History

First Known Use

1814, in the meaning defined above

Time Traveler
The first known use of side effect was in 1814

Browse Nearby Words

Cite this Entry

“Side effect.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/side%20effect. Accessed 2 Jul. 2025.

Kids Definition

side effect

noun
: an often harmful and unwanted effect (as of a drug) that occurs along with the basic desired effect
the environmental side effects of using chemicals to kill pests

Medical Definition

side effect

noun
: a secondary and usually adverse effect (as of a drug)
toxic side effects
a side effect of drowsiness caused by antihistamines

called also side reaction

Last Updated: - Updated example sentences
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