Epinephrine itself, sure. Epipens, though? Looking at https://en.wikipedia.org/wiki/Epinephrine_autoinjector , I see "In 2009, Teva Pharmaceuticals filed an ANDA to market a generic EpiPen in collaboration with Antares Pharma Inc, a maker of injection systems; Pfizer and King sued them for infringing US Patent 7,449,012 that was due to expire in 2025", and "In 2010, Pfizer and King sued Novartis' Sandoz generic unit for patent infringement after Sandoz submitted an ANDA to sell a generic EpiPen."

You need a delivery mechanism that can be used quickly and reasonably safely, ideally by someone in the early stages of anaphylaxis. Taking out a vial and a syringe, and carefully extracting the epinephrine from the vial with the syringe, are not things you'd want to be doing under those circumstances. Hence the invention of better approaches.

But epipens were originally "brought to market in 1983". How are there still active patents for it? "Kaplan continued to improve his designs over the years, filing for example US Patent 6,767,336 in 2003." I wonder if the new patents cover the 1983 devices. If so, that seems like an obvious abuse of the system: keep filing a new patent for different aspects of or variations on the device, and you can multiply the duration of your monopoly grant.