does epipen work underwater, through a nalprene suit?

Yes it will go through nalprene, but will it reach your muscle? Wet suits can range form 3mm-7mm thick depending on the temperature of the water. I'm not sure the exact measurement of the epi-needle It looks like it about 1.5-2cm. See if you can measure yours. The box should also say what type of temperature to store it at. How cold is the water you will be diving in. Lot's of things to consider. If you go make sure you have a dive partner at all times! This person should be instructed on what to do and how to use the epi-pen. Make sure you take quite a few with you, in case of dropping one, needing a larger dose etc. Alos if used under water make sure that you get the injection sites checked afterwards for redness, swelling, as they could be a sign of infection (lots micoorganism in the ocean). Also ask a doctor if it would be a good Idea to take some benadryl before hand for prevention, although the drowsiness might not be fun.

Call the pharmacist that filled you Rx. I was told that my daughter's Epi Pen would go through her winter coat with no problem and it's fairly thick. It doesn't say on the website if it's affected by water, just to keep it out of extreme temps (59-86 F or 15-30 C), and out of direct sunlight.

Epi will work no matter what environment your in. As for the nalprene suit, I dont know anything about scuba diving or it's gear. If the needle will puncture the suit and you skin you should be good.