A side effect is an unintended consequence of a medication or medical treatment beyond its primary therapeutic purpose. Side effects can range from mild (drowsiness, dry mouth, nausea) to serious (organ damage, allergic reactions). Healthcare providers weigh potential side effects against therapeutic benefits when prescribing medications. Pharmacists explain common side effects when dispensing prescriptions. Health Canada reviews and approves medications partly based on side effect profiles, requiring manufacturers to list known side effects in product information. Patients should report unexpected side effects to their healthcare providers. Some side effects diminish over time while others may require medication changes or additional treatment to manage.