system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:what would happen if someone injected themselves with a "Eppie Pen" if they didn't need it?
gpt
An epipen injects you with a dose of epinephrine (adrenaline). Your heart beat is going to get crazy high and your breathing might deregulate. That is why you need to get to the hospital ASAP after any injection with an epipen. Additionally, epinephrine constricts the blood vessels around the injection site, so depending on where you got injected with it, they are going to want to monitor that you are still getting enough blood in that location. 

*Edit*: One other thing. This above is what happens if it has been correctly injected in a muscle. If you accidentally inject it in a vein, you might just die from ventricular tachycardia. Which is your heart beating so quick that shocking you with two giant paddles seems like a good solution.