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

They were looking for clues that could eventually reduce the need for pain medications that carry significant side effects.

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It did so without causing major bleeding, a side effect of other blood thinning medications, Bayer said.

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Importantly, the therapy did not spread widely throughout the body, helping reduce the likelihood of unwanted side effects.

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These therapies can also be expensive and may trigger immune-related side effects, underscoring the need for safer, low-cost options that are easier for patients to access.

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There can be side effects - such as redness, swelling and bruising but these tend to be temporary.

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Related Words

• aftereffect 
• reaction