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

Shares of weight loss drug maker Zealand Pharma plummeted as much as 23% on Monday after new data on its experimental medicine raised concerns over its potential side effects. —Elsa Ohlen, CNBC, 8 June 2026

Boukpessi stopped taking the drug after his severe side effects but ultimately decided to try it again at a smaller dose. —Daniel Gilbert, CBS News, 8 June 2026

Common side effects of increasing fiber too quickly include bloating, abdominal pain, diarrhea and excess gas, according to UC Health. —Ryan Brennan june 8, Kansas City Star, 8 June 2026

The pulses are designed to normalize the nerve messaging from the brain to the stomach to relieve symptoms of nausea and vomiting without side effects. —ABC News, 6 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