EpiPen is for the emergency treatment of anaphylactic allergic reactions. These situations can be extremely serious. EpiPen contains adrenaline which is a hormone naturally secreted by the body in response to stress. In acute allergic reactions, it works by improving blood pressure, heart, and respiratory function, and reduces swelling. Sometimes a single dose of adrenaline may not be enough to completely reverse the effects of a severe allergic reaction. For this reason, you may be prescribed more than one EpiPen to keep on hand for an emergency.