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

Over time, some people even begin experiencing side effects, emotional numbness or a feeling that the medication is no longer helping in the same way. —Daryl Austin, USA Today, 23 June 2026

The pulses are designed to normalize the nerve messaging from the brain to the stomach to relieve symptoms of nausea and vomiting without side effects. —ABC News, 22 June 2026

Wellness was not an end goal but rather a helpful side effect of achieving his other purposes. —Ezekiel J. Emanuel, Fortune, 21 June 2026

The 8,000Hz polling rate feels more responsive than the 1,000Hz polling rate in most gaming mice, but this has the unfortunate side effect of cutting into the V2 Pro Ultralight's battery life in a big way. —Alice Jovanee, PC Magazine, 20 June 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