Can one who takes daily medicine that helps one concentrate better in all areas of life take this medication on shabbos, or do we say that since if not taken one just wont be able to concentrate on davening and learning etc. then it is better not to take it?
It is only permitted to take medicine on Shabbos if refraining from taking the disturbance would cause a severe disturbance to a person’s function — the inability to concentrate well would not be included in this definition. However, with regard to daily medicines some poskim permit taking the medicine even on Shabbos, and this may be relied where necessary.
In addition, there are poskim who permit medication that is not related specifically to “healing” an illness, though others have disputed this ruling based on the Mishnah Berurah’s ruling that anything which is not “food for healthy people” is prohibited.
Sources: Shulchan Aruch and Mishnah Berurah, Orach Chaim 328:1; Shemiras Shabbos Kehilchasah 34:16; Tzitz Eliezer vol. 8, no. 15 (kuntress meshivas nefesh chap. 15); Be’er Moshe vol. 1, no. 33.