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

To this day, doctors can't explain why Lemons never experienced physical or mental side effects from the oxygen deprivation. —Sydney Bucksbaum, EW.com, 28 Feb. 2025

However, everyone responds to it differently, and there may be risks for some people, such as the following: Common side effects: Water retention is common with the loading dose of creatine or when taken at high doses. —Sarah Anzlovar, Ms, Rd, Verywell Health, 27 Feb. 2025

Also, lion’s mane is not without side effects—headaches, digestive discomfort and allergic reactions are somewhat common. —Scott Travers, Forbes, 26 Feb. 2025

Low platelet counts can be caused by a number of things, including side effects from medicines or infections, according to the AP, which cited the U.S. National Institutes of Health. —Mark Joseph, Newsweek, 23 Feb. 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