How an EpiPen Works

How an EpiPen Works
How an EpiPen Works (Image: Wikicommons: CC License SA BY: Sean Williams, Wikicommons: CC License 2.0 BY: Katia)

Using an EpiPen

The active ingredient, epinephrine, in the EpiPen belongs to a class of drugs known as sympathomimetics. These medications mimic the actions of hormones or other naturally occurring substances released in the body in response to stress. These chemicals raise blood pressure, increase heart rate and constrict blood vessels, which is why epinephrine is used to alleviate the most severe allergic reaction, anaphylaxis.


Some people with allergies do not just sneeze or cough in reaction to the allergen. They experience anaphylaxis in reaction to insect bites, contact with latex or food allergies. During anaphylaxis, the patient experiences a sudden drop in blood pressure, difficulty in breathing and swelling in the face and throat. These signs indicate that immediate medical attention with an epinephrine injection via an Epi-Pen is necessary.

A bee sting can cause a severe allergic reaction: anaphylaxis.
A bee sting can cause a severe allergic reaction: anaphylaxis.

How an Epi-Pen Reverses Anaphylaxis

An Epi-Pen conceals a needle pre-loaded with the appropriate amount of epinephrine for one's body weight. The patient will not use an Epi-Pen until he experiences a severe allergic reaction or anaphylaxis. At that time, the patient unscrews the safety cap from the end of the Epi-Pen, removes the auto-injector from the plastic sleeve, and holds the unit in his fist. The patient must swing the Epi-Pen next to his outer thigh until the black tip hits the thigh at a 90-degree angle. Holding the Epi-Pen next to the thigh for 10 seconds allows the epinephrine to fully empty from the needle. Massaging the site helps to speed the drug into the bloodstream. Injecting epinephrine directly into the thigh delivers this medicine throughout the body faster than taking an oral dose, which would have to be digested before entering the bloodstream.

The epinephrine then raises dangerously low blood pressure by tightening the blood vessels. Epinephrine in the blood eases breathing by helping the lung muscles relax and reduces swelling in the throat and face. Then the heart rate increases as blood pressure rises, delivering the epinephrine faster to the whole body. Once the symptoms of anaphylaxis or severe allergic reaction ease, the patient must still go to an emergency room for continued treatment and evaluation by a medical professional in case a secondary reaction occurs once the the Epi-Pen injection wears off.

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