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 trials, about 70% of patients reached clear or almost-clear skin, with side effects similar to placebo. — Leslie Baumann, Miami Herald, 3 Sep. 2026

Almost all participants reported side effects, with severe side effects observed in 54% of individuals. — Mary Kekatos, ABC News, 3 Sep. 2026

Taking calcium supplements could exacerbate this side effect. — Jennifer Lefton, Verywell Health, 3 Sep. 2026

The side effects of Diamox can range from strange to unpleasant. — Katie Hill, Outdoor Life, 3 Sep. 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