EpiPen and EpiPen Jr Auto-Injectors are used along with emergency medical treatment to treat life-threatening allergic reactions caused by insect bites or stings, foods, medications, latex, and other causes. 

EpiPen is in a class of medications called alpha- and beta-adrenergic agonists (sympathomimetic agents). It works by relaxing the muscles in the airways and tightening the blood vessels.

EpiPen comes as a pre-filled automatic injection device containing a solution (liquid) to inject under the skin or into the muscle in the outer side of the thigh. It is usually injected as needed at the first sign of a serious allergic reaction. Use EpiPen exactly as directed; do not inject it more often or inject more or less of it than prescribed by your doctor.

Some common side effects of EpiPen include difficulty breathing, nausea, vomiting, sweating, and headache.