side effect

noun

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.

any accompanying or consequential and usually detrimental effect:

the side effects of air pollution.

Also, side-effect.

Origin

1880-85

Examples from the web for side effects

But nearly all failed because of the difficulties of getting a working gene into cells without also causing harmful side effects.
There were some side effects to the development of our skull position.
Half of those who participated in the poll expressed concern about possible side effects.
The side effects of unrestrained credit growth turned out to be devastating.
As far as other treatments, it depends on side effects.
Serious chemotherapy side effects can also occur and may vary depending on the specific drugs used.
Anticholinergics can have distressing side effects, notably dry mouth.
Even patients' level of side effects from arthritis medication seem determined by those patients' beliefs about those medicines.
Both of these things have ugly side effects, of course.
side effects may include intense pain, extreme vomiting, and absolutely terrifying visions.

British Dictionary definitions for side effects

noun

any unwanted nontherapeutic effect caused by a drug Compare aftereffect (sense 2)

any secondary effect, esp an undesirable one

Word Origin and History for side effects

also side-effect, 1884, from side (adj.) + effect (n.). Medical use, with reference to drugs, is recorded from 1939.

side effects in Medicine

side effect n.
A peripheral or secondary effect, especially an undesirable secondary effect of a drug or therapeutic regimen.