Meaning of “side effect” - Learner’s Dictionary

side effect

noun [ C ] uk us /ˈsaɪdɪfekt/
MEDICINE

another effect that a drug has on your body in addition to the main effect for which the doctor has given you the drug:

Headaches are one side effect of this drug.
RESULT

(Definition of “side effect” from the Cambridge Learner’s Dictionary © Cambridge University Press)