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

Teeth Staining Some people may experience more gastrointestinal side effects with the oral dosage form of iron and opt for liquid iron instead. —Ayesha Gulzar, Verywell Health, 26 Sep. 2025

Concerns online have stirred conversations about whether the deterioration of oral health is a potential side effect of semaglutides. —Kaleigh Werner, Footwear News, 26 Sep. 2025

So far, the drug, which was approved in 2002 to address side effects of chemotherapy, has undergone limited testing for the treatment of autism. —Lisa Jarvis, Mercury News, 25 Sep. 2025

The most common side effects in kids are stomach issues like nausea, vomiting, diarrhea and loss of appetite. —Brenda Goodman, CNN Money, 24 Sep. 2025

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