What is the length of the effects of an epi-pen?

Minutes: Epinephrine when used for anaphylaxis generally lasts a very short time. In general, if you use one uses their injectable Epinephrine for a severe allergy reaction they must call 911 and get immediate help. The reason being is that the reaction may become more severe, last longer than expected or come back again. All of these scenarios require further care in the hospital setting.

15-20 minutes: The effects of an epi-pen wear off after 15 to 20 minutes.

ER in a can: I agree with drs. Murphy & rhein. In an episode of life-threatening anaphylaxis Epinephrine buys you the time to call 911 & begin to receive comprehensive emergency treatment. Once you get over the squeamishness of injecting yourself or your child it's an incredibly safe & effective drug. Benadryl (diphenhydramine) doesn't hold a candle to epi. Epi may only last 15 minutes but those minutes are critical for life.