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

Patients will then have to be followed by hospital monitoring boards and serious side effects or other issues will have to be reported to both Revolution Medicines and the FDA. —Mary Walrath-Holdridge, USA Today, 1 June 2026

People in the trial reported similar side effects to those from mRNA Covid vaccines — flu-like symptoms including chills and headaches — that only lasted a couple of days. —Kaitlin Sullivan, NBC news, 1 June 2026

Despite seeing success on the GLP-1, Madden experienced common side effects and rising costs that prompted her to seek out other options. —Grace Gavilanes, PEOPLE, 1 June 2026

Why Ozempic Users Face Extra Cautions For people taking Ozempic or other GLP-1 medications, alcohol can amplify side effects already common with the drugs. —Samantha Agate, Kansas City Star, 1 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