side effect

Or side-ef·fect

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.

side effect

noun

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

2. any secondary effect, esp an undesirable one

Word History and Origins

Origin of side effect¹

First recorded in 1880–85

Example Sentences

Enhancing the drug’s skin permeability could make treatments more efficient, reduce application frequency, and possibly lower side effects related to overuse.

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It is currently used to help patients with side effects from chemotherapy.

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The drug, chemically related to vitamin B9, was typically used to ward off side effects of chemotherapy.

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Medical products that haven’t yet been approved might or might not be effective in treating a condition, and could cause unexpected and serious side effects, an FDA representative said.

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The researcher argues that natural and accessible treatments should gain ground in the fight against obesity, especially as alternatives to expensive medications that often have side effects.

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Related Words

• aftereffect 
• reaction