I been given a epipen (epinephrine) I was wonrdring why I have to go hosiptal after useing it and what would they do at the hosiptal?

Rebound phenomena. Emergency room followup after using an epi-pen is a good idea. The Epinephrine in the pen can provide life saving intervention to ward off the effect of an allergic exposure, but the pen may ware off within minutes or hours and any residual trigger (food, sting venom, etc.) could start it over.Iv or injected steroids or longer lasting meds may be needed to treat you.