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

In addition to that very concerning laundry list of potential side effects, people are currently buying Melanotan II and its peptide peers from unregulated online sources, also known as the gray market. — Kara Nesvig, Allure, 9 July 2026

Too little of either nutrient can lead to weak, brittle bones, and too much can cause unwanted side effects. — T'keyah Bazin, Verywell Health, 9 July 2026

Those side effects are common with GLP-1 medications, and finding foods that go down easily can be a challenge during the first weeks on the drug or after a dose increase. — Lauren Jarvis-Gibson july 8, Fort Worth Star-Telegram, 8 July 2026

In a March letter to the state, 11 board members called for the program to be halted, citing the risks of automatically renewing medicines that can have side effects or drug interactions. — ABC News, 6 July 2026

Word History

First Known Use

1814, in the meaning defined above

Rhymes for side effect

• aftereffect
• interconnect
• affect
• aspect
• bedecked
• bisect
• collect
• connect
• correct
• deflect
• detect
• direct

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