sideeffect

Side effect, sometimes written side-effect, refers to an effect of a medical treatment that is not the primary intended therapeutic outcome. Side effects can accompany many drugs, vaccines, or other interventions. They range from mild and predictable to severe and uncommon, and they may be dose-dependent or occur unpredictably in some individuals.

Side effects are distinct from adverse drug reactions in that the term describes any secondary effect of a treatment, whereas adverse drug reactions emphasize harm or injury. In practice, many side effects are also considered adverse events if they are unpleasant or dangerous. Not all side effects are harmful; some may be tolerable or transient, while others require medical attention, dose adjustment, or change of therapy.

Common examples include digestive disturbances (nausea, vomiting, diarrhea), sedation or dizziness, and dry mouth. Serious side effects, though rarer, can include allergic reactions, liver or kidney injury, or cardiac effects. The likelihood and severity of side effects depend on factors such as dose, duration of exposure, patient age, genetics, concurrent medications, and underlying conditions.

Evaluation and reporting of side effects occur through clinical trials and pharmacovigilance systems after a product is marketed. This information informs labeling, risk mitigation, and patient counseling. Management strategies focus on reducing exposure, adjusting timing or formulation, treating symptoms, or switching to safer alternatives.