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

For dog owners considering CBD supplements for their pups, the researchers stress the importance of selecting a reputable brand and monitoring dosage carefully, as CBD can cause side effects such as gastrointestinal issues and diarrhea. —Maria Azzurra Volpe, MSNBC Newsweek, 28 Nov. 2025

The results did not indicate any major side effects or immunity depletion, the scientists noted. —Angelica Stabile, FOXNews.com, 28 Nov. 2025

These side effects subside after your gut gets used to the probiotics. —Stephanie Brown, Verywell Health, 27 Nov. 2025

In other words, a law designed to democratize the market could end up reinforcing its inequalities, a side effect already seen in other countries. —Caio Delcolli, IndieWire, 26 Nov. 2025

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