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

Reducing the Burden of Side Effects Along with lifestyle changes that may affect the disease’s progression, a number of complementary therapies may help patients with prostate cancer address the symptoms of their disease and the side effects of treatment. —Markham Heid, TIME, 13 Dec. 2024

Expulsion Expulsion of the IUD is another less common side effect of copper IUDs. —Wendy Wisner, Health, 11 Dec. 2024

These side effects can last from a few weeks to months, depending on the person. —Tori Crowther, Allure, 11 Dec. 2024

The trials, of which many are in South Florida, typically require participants to acknowledge potential high-risk side effects and meet the eligibility criteria. —Cindy Krischer Goodman, Sun Sentinel, 10 Dec. 2024

Word History

First Known Use

1814, in the meaning defined above

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