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

But hybridization had its side effects. —Jackie Flynn Mogensen, Scientific American, 14 Feb. 2026

GLP-1s often come with side effects, most commonly gastrointestinal, an improved tolerability profile is another key differentiator that companies are looking at with amylin treatments that target another gut hormone, alongside treating related conditions. —Elsa Ohlen, CNBC, 13 Feb. 2026

Stop use of any supplements if serious side effects occur. —Bestreviews, Chicago Tribune, 13 Feb. 2026

Gulati said common side effects of the drug are nausea and constipation. —Livi Stanford, Hartford Courant, 12 Feb. 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