Adverse drug effects, also called adverse side effects or adverse drug events, are unwanted reactions that people have to drugs. The more severe drug side effects are more appropriately termed adverse drug reactions. The definition of adverse drug effects does not include drug abuse, or intentional or accidental drug overdose. Most adverse drug effects are relatively mild and disappear when the drug is stopped, the dose is reduced or the body becomes used to the drug. Common adverse drug reactions include: digestive disturbances, a bloating sensation, constipation, diarrhea, loss of appetite and nausea.
Severe adverse drug effects can include: peptic ulcers or bleeding from the stomach from corticosteroids taken by mouth or injection from hydrocortisone or prednisone; anemia from antibiotics such as chloramphenicol; decreased production of white blood cells from certain antidepressant drugs such as clozapine; liver damage from excessive doses of acetaminophen; kidney damage due to repeated excessive use of non-steroidal anti-inflammatory drugs. One of the most severe reactions – and one that may prove fatal – is anaphylaxis, an allergic reaction. Symptoms of anaphylaxis include hives, swelling of the face or throat, wheezing, light-headedness, vomiting and shock.