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.
Some appeals to stay on Zepbound have been approved and other people have been able to switch to Wegovy with only mild side effects, but the change has been disruptive for many patients and their doctors. Deidre McPhillips, CNN Money, 5 Sep. 2025 The mixture is generally safe in small amounts, but excessive intake can cause side effects, such as tooth erosion and stomach upset. Lindsay Curtis, Verywell Health, 4 Sep. 2025 Other common side effects included nausea and headaches. Ken Alltucker, USA Today, 4 Sep. 2025 Serious side effects were rare. Dr. Christian S. Monsalve, ABC News, 4 Sep. 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 9 Sep. 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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