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

However, the study found no increase in serious side effects, including pancreatitis, among cancer patients taking the medications. —Anthony Thompson, USA Today, 23 May 2026

Burnout, emotional fatigue, and cognitive overload are no longer side effects of volatility. —Dr. Nadya Zhexembayeva, Forbes.com, 23 May 2026

But participants experienced high rates of side effects, and about 11% discontinued due to adverse events, raising questions about how appealing the treatment would be. —Theresa Gaffney, STAT, 22 May 2026

But high doses from supplements can lead to side effects like diarrhea, nausea, and stomach cramping. —Morgan Pearson, Verywell Health, 21 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