Definition of side effect noun from the Oxford Advanced Learner's Dictionary

     

    side effect

     noun
    noun
    BrE
     
    ; NAmE
     
    [usually plural] Medication
     
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  1. 1an extra and usually bad effect that a drug has on you, as well as curing illness or pain The drug has few side effects. Side effects include skin rashes and nausea. See related entries: Medication
  2. 2an unexpected result of a situation or course of action that happens as well as the result you were aiming for Opponents of the policy fear that it could have unfortunate side effects on the economy.
  3. Extra examples The medication can have adverse side effects on the patient. The patient suffered severe side effects from the drug. The treatment has some unfortunate side effects. This drug has no known side effects.
See the Oxford Advanced American Dictionary entry: side effect