Definition: An adverse reaction is an undesirable side effect due to the use of a medication. Adverse reactions may include symptoms, such as muscle pain or nausea; changes in laboratory tests, such as abnormal liver function tests; and, changes in other measures of your body’s function, such as your pulse, blood pressure and electrocardiogram (ECG).
Also Known As: side effect
Examples:An adverse reaction to some statin drugs (such as Lipitor, used to treat high cholesterol) is muscle pain. An adverse reaction to some antidepressant medication (such as Zoloft, used to treat depression) is erectile dysfunction.