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

Others place greater importance on independence, energy levels or minimizing side effects. —Lauryn Higgins, Flow Space, 15 June 2026

To avoid this side effect, wait a couple of hours to enjoy a carbonated drink after taking your supplements. —Carrie Madormo, Verywell Health, 15 June 2026

Yet Griffin’s businesses are not doing these things as a public service—that’s a side effect. —Gary Sernovitz, New Yorker, 15 June 2026

Occasional leakage, especially in children, whose inhibitory systems are still maturing, is less a feature than a side effect of running such a complicated piece of hardware every night without maintenance windows. —Scott Travers, Forbes.com, 14 June 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