How does EpiPen® work during a severe allergic reaction?

During anaphylaxis, airways constrict and blood vessels dilate and become more permeable, which can lead to loss of fluid volume from within the vessels and low blood pressure (hypotension). Adrenaline acts on different parts of the body to constrict blood vessels and relax bronchial muscle, helping to reduce bronchospasm, wheezing and dyspnoea. Adrenaline also alleviates pruritus (itching), urticaria (rash), and angioedema (swelling) and may be effective in relieving gastrointestinal and genitourinary symptoms associated with anaphylaxis because of its relaxant effects on the smooth muscle of the stomach, intestine, uterus, and urinary bladder.