March 8, 2017

How Do EpiPens Work?

EpiPen has made a splash in the headlines in recent months. Last summer, the pharmaceutical company Mylan drew widespread criticism when it was revealed that a 500% price hike had been placed on the epinephrine autoinjector. After Congressional investigations, Mylan agreed to introduce a cheaper generic version of the drug, as well as fund programs to help patients afford the costs.

An EpiPen, with its safety cover. Source: Tokyogirl79 (Wikimedia Commons)

But the damage has already been done: since the beginning of 2017, physicians have been prescribing alternatives to EpiPen at a rate 6X higher than in 2016. Without insurance, a generic version called Adrenaclick costs just $10 for a two-pack at CVS.

A young boy with anaphylaxis. 
Source: James Heilman, MD 
So how do EpiPens, and other brands of epinephrine autoinjectors, work in the first place?

Millions of people keep epinephrine autoinjectors on hand due to their risk of anaphylaxis. Anaphylaxis is a serious type of allergic reaction — most commonly to particular foods, animal stings or bites, and medications — that can start within minutes of exposure to the allergen. Symptoms include shortness of breath, throat or tongue swelling, vomiting, lightheadedness, and a drop in blood pressure.

Why such a severe reaction? In response to the the allergen, inflammatory mediators such as histamine cause contraction of smooth muscles (such as the lungs), blood vessel dilation and fluid leakage, and changes in heart rate. A person can die from anaphylaxis if their heart stops beating, or if they are unable to breathe due to swelling of the airway.

EpiPens work by rapidly injecting a dose of epipinephrine (also called adrenaline), which reverses the effects of anaphylaxis.

Epinephrine. Source: Roland Mattern (Wikimedia Commons)
Epinephrine, which plays an important role in our fight-or-flight response, relaxes the smooth muscles of the airways and lungs, and rapidly increases blood pressure by constricting blood vessels. (It's the same hormone that makes us feel like we can run a marathon when, instead, we have to sweat through a public speech to a large, scary audience.) The pen is injected directly into the thigh muscle, as the intramuscular route is faster than subcutaneous administration (like how insulin is delivered).

Have you used an epinephrine autoinjector before? What was the experience like? Let me know in the comments.


  1. I used an EpiPen about 16 years ago (I was 51) on a river trip floating down the Main Salmon in Idaho, it was an 8 day trip and on the second day I was bitten by a wasp/hornet during one of the breaks for lunch. They are notorious on the River...I was groggy and fell asleep through several big rapids. The reason I am writing is that since that injection I have been stung/bitten by wasps/hornets a couple of times (a few years after the river trip) and did not go into anaphylactic shock. That was a good thing b/c I did not have an EpiPen available at the time. In my late 20's I had had a couple of very serious reactions to bites/ strings so that is why I got an EpiPen in the first place. Did that injection of adrenaline have anything to do with not having a reaction the next time I was bitten? Just wondering...I am a therapist in Boise Id. and I LOVE educating people about their brains and the connection to emotions, flight, flight, freeze etc. Keep up the good work...I am still waiting for an answer about that happens to the hippocampus during anesthesia! Damiana

    1. Hi Damiana, thanks for your comment. I have not forgotten your question on anesthesia! It's interesting that you used an EpiPen for awhile, but later did not react to a bite. Because the epinephrine injection is so temporary, I wouldn't think that it prevented a later reaction. I am aware that people can "outgrow" allergies, to a degree, though outgrowing something as severe as anaphylaxis seems extreme! Was it perhaps a different type of bite/sting?


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