Q. If one is in a place over Shabbos where there is no eruv, are they permitted to carry an EpiPen since it is pikuach nefesh (life danger)?
A. Shemiras Shabbos Kehilchoso (40: 7) writes that an ill person who was ordered by his physician not to leave home without taking certain necessary medicines, or a candy (for diabetes) etc. and there is no local eruv. he may be permitted to carry, under certain conditions. Firstly, the streets he is going to walk by should not be considered a proper reshus horabim. (They are less than 16 amos or about 8m. wide. It is not open on both ends as it runs across town. According to some Poskim, less than 600,000 travelers use it every day). The reason of his walking on the street is that he is performing a necessary mitzva, such as going to shul or to a Torah shiur. Additionally he should be carrying the items in an unusual way or with a shinui, such as under his hat or inside his socks and not more than the items that are needed.
Nishmas Avrohom (1: p. m125) quoting R.Z. Auerbach zt”l rules similarly. Mishne Halochos (7: 56) is even more lenient under the above conditions as he permits going out with the needed medicine if he feels he needs to take a walk for his health.
However, Tzitz Eliezer (13: 24) is stringent and does not permit carrying the needed medicine even when going to shul. He recommends that one who needs the medicine should before Shabbos take it and keep it in shul or any other place he is planning to visit, otherwise, one should remain at home.
Horav Shlomo Miller’s Shlit’a opinion is also to be stringent. Nevertheless, the Rov may permit, if one prepares before Shabbos, under the supervision of a competent rabbinical authority a proper belt, in which a single EpiPen is needed as an essential part of the buckle. This being similar to the customary house key carried in a similar way in locations where there is no eruv.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a