An epinephrine autoinjector (or adrenaline autoinjector, also known by the trademark EpiPen) is a medical device for injecting a measured dose or doses of epinephrine (adrenaline) by means of autoinjector technology. It is most often used for the treatment of anaphylaxis. The first epinephrine autoinjector was brought to market in 1983.

Epinephrine autoinjectors are hand-held devices carried by those who have severe allergies; the epinephrine delivered by the device is an emergency treatment for anaphylaxis.

When anaphylaxis is suspected, epinephrine solution should be given as soon as possible as an intramuscular injection, in the middle of the outer side of the thigh, which corresponds to the location of the vastus lateralis muscle. The injection may be repeated every 5 to 15 minutes if there is insufficient response. A second dose is needed in 16–35% of episodes with more than two doses rarely required; in around 80% of the cases where a second dose is administered, it is by a medical professional. It is not clear which are the people who might need a second injection at the outset. The intramuscular route is preferred over subcutaneous administration because the latter may have delayed absorption. Minor adverse effects from epinephrine include tremors, anxiety, headaches, and palpitations.

The epinephrine in autoinjectors expires after one year. A study in rabbits showed that intramuscular epinephrine has decreased effectiveness after it expires; that study also recommended that if the drug in an expired device has not started to precipitate (if the solution is not cloudy and has no particles in it) using the expired device is better than no injection at all in an emergency situation.

The devices contain a fixed dose of epinephrine and a spring-loaded needle (or, in the case of AuviQ, a CO₂-driven needle) that exits the tip or edge of the device and penetrates the recipient's skin, to deliver the medication via intramuscular injection.

People to whom epinephrine autoinjectors are prescribed need to be trained how to use the specific device prescribed. The rate of unintentional injections using these devices is unknown but a 2009 review found that the rate is increasing. Unintentional injections are delivered to a finger or thumb around 90% of the time; they cause intense pain locally but usually completely resolve. The cause of unintentional injections has been attributed to design flaws, where the device is mistaken for a pen or the user mistakes which end of the device contains the needle.

The European Medicines Agency conducted a review of the safety of devices then on the market and found several factors that determine whether the devices successfully deliver drug into muscle, including "needle length, the thickness of fat under the skin, the way the auto-injector works (e.g., if it is spring loaded or not), the angle at which the device is placed on the skin and the force used to activate the device as well as how well the user follows the instructions for injection." It found that how well the user was trained was the most important factor determining successful delivery, and requested companies to develop better training materials for doctors and people to whom the devices are prescribed.

In 2013, emergency physician Seth C. Hawkins and coauthors published a technique for obtaining multiple additional doses of epinephrine from used, single dose autoinjectors EpiPen and Adrenaclick. It was emphasized this was an emergency adaptation of the intended design for austere environments when no additional epinephrine was available. In 2016, Robinson and Lareau published a similar technique adapted to used AuviQ autoinjectors.