side effect

noun

Synonyms of side effectnext
: 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.
None of the side effects appeared at higher rates among the group that had received both vaccinations. — Theresa Gaffney, STAT, 30 June 2026 Plus, some common pain medicines can come with side effects or safety concerns, especially when used long-term. — Tom Gavin, EverydayHealth.com, 1 July 2026 Possible side effects from zinc include nausea, vomiting, and stomach pain. — Kirstyn Hill, Health, 1 July 2026 Taking more than your body needs can actually cause vitamin toxicity, leading to side effects that range from mild discomfort to serious health problems. — Anna Giorgi, Verywell Health, 3 July 2026 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

Rhymes for side effect

See All Rhymes for side effect

Browse Nearby Words

side drum
side effect
side-end lines
See all Nearby Words

Cite this Entry

“Side effect.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/side%20effect. Accessed 7 Jul. 2026.

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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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