Is it "side affects" or "side effects"?

Contexti

Pharmaceutical labels, medical patient inserts, and health articles use this phrase constantly — which makes the typo conspicuous when it slips through. The compound noun side effect has been in use since the 1880s and is one of the most fixed idioms in English medical writing.

A little moreii

Side effects are the unintended results a medicine or decision produces — they are nouns you can point at. Affect is a verb, so "side affects" reads as if the sides are doing something. If you can put "the" in front and it still works, the word is effect.

Examplesiii

Watch foriv

The full entryv

More quick answersvi

• → Is "affect" a verb? Yes. "Affect" is almost always a verb, meaning to influence or change something: the weather affected our plans.
• → Is "effect" a noun? Yes. "Effect" is almost always a noun — the result of something: the effect was immediate.
• → Is it "affect" or "effect"? Use affect for the verb (influence). Use effect for the noun (result).
• → Is it "deeply affected" or "deeply effected"? "Deeply affected." The word describes an action done to someone — that's the verb affect.