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

What are the side effects of Ambien? Ambien's side effects include nausea, vomiting, muscle cramps and diarrhea. —Charles Trepany, USA Today, 22 July 2025

But the side effects were often brutal — nausea, fatigue and other toxic reactions made the drugs intolerable for many. —Timothy Holtz, Sun Sentinel, 22 July 2025

At best, this annoying little side effect can limit your performance. —Jeanne Ballion, Vogue, 21 July 2025

Mild side effects can include diarrhea, nausea, and abdominal cramping.6 Taking too much magnesium for too long can lead to hypermagnesemia, a condition in which blood magnesium levels are too high. —Ashley Wong, Health, 21 July 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