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

And neither happens easily in organizations that treat the human experience of change as a side effect to be managed rather than a reality to be understood. — Maria Ross, Forbes.com, 31 July 2026

All supplements may cause side effects, drug interactions, or pose a risk to specific populations. — Megan Nunn, Verywell Health, 30 July 2026

Its results have sparked a flurry of activity as physicists try to determine whether the conflicting measurements are a side effect of different experimental procedures, or a sign that new particles are popping up after all. — Matt Von Hippel, Quanta Magazine, 29 July 2026

That hour made clear that isolation is not an inevitable side effect of hospitalization, but rather a consequence of a care delivery structure that can, and should, change. — Anna Tsioulias, STAT, 29 July 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