side effect

American  

Or side-effect

noun

1. any effect of a drug, chemical, or other medicine that is in addition to its intended effect, especially an effect that is harmful or unpleasant.

2. any accompanying or consequential and usually detrimental effect.

   the side effects of air pollution.

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side effect British  

noun

1. any unwanted nontherapeutic effect caused by a drug Compare aftereffect

2. any secondary effect, esp an undesirable one

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Etymology

Origin of side effect

First recorded in 1880–85

Example Sentences

That means it can influence the gut microbiome without affecting the rest of the body, helping to avoid toxicity and unwanted side effects.

From Science Daily

Despite these benefits, many patients experience unwanted side effects.

From Science Daily

This required strong antibiotic treatment which itself had serious side effects.

From BBC

Patient leaflets on weight-loss injections state that gallstones are a "common" side effect, and in medical trials the injections also sometimes led to inflammation of the gallbladder.

From BBC

"Busting up amyloid plaques hasn't worked that well, and there are a lot of side effects," such as headaches and brain bleeding, Shatz said.

From Science Daily

Related Words

• aftereffect
• reaction