Is it permissible to take a pill on Shabbos for performance enhancement (caffeine pills or pills to delay הוצאת זרע due to pre-mature issues)?
Caffeine pills etc. seem to be considered healing by the poskim and therefore should not be taken on Shabbos. There are pills however that have a long lasting effect and can be taken from before Shabbos
Shulchan Shlomo Siman 321-23, also see Shevet Halevi 8-287, Sefer Refuah Bshabbos ( R’ Bodner) pg. 36, 342.