A side effect is a new symptom that occurs when you take a medication, either because of the medication or because of the way you take it (such as by injection, IV, by mouth, or by patch). The label on your medication and the paper insert that comes with the medication will list common side effects. Common side effects for many medications include feeling sleepy, gaining weight, coughing, or having stomach or bowel problems. Most side effects often are not serious, but you should always talk to your doctor or pharmacist if you have questions or concerns about your medication’s side effects.