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

The side effect of this entire pattern has been a warmer Delta breeze carrying with it just a bit more humidity in the evening for Sacramento. — Sean MacAday, Sacbee.com, 24 July 2026

The study also showed that the muscle side effects might be separate from statins’ cholesterol-lowering effects. — Mark Gurarie, Verywell Health, 23 July 2026

The drugs themselves can have severe side effects, such as hair loss and cracking, painful, dry skin. — Susanne Rust follow, Los Angeles Times, 23 July 2026

Living longer can come with costs Every treatment can cause side effects. — Dr. Jamin Brahmbhatt, CNN Money, 23 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