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

That incisive clarity has had an unintended side effect on the novel’s film and TV legacy ever since. —Alison Foreman, IndieWire, 4 May 2026

There is also some preliminary evidence that suggests that CBD could be used to treat schizophrenia with fewer side effects than antipsychotic drugs, which can cause weight gain and neurological symptoms, for example, Grant says. —Jackie Flynn Mogensen, Scientific American, 4 May 2026

The hair loss from GLP-1s is one of the most significant side effects that the beauty industry is watching, according to Audrey Depraeter-Montacel, Accenture's global beauty industry lead. —Laya Neelakandan, CNBC, 2 May 2026

This potential side effect appears to be shaping consumers’ spending habits. —Melissa Rudy, FOXNews.com, 1 May 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