If someone has sinus headaches occassionally, is it permitted to take a pain reliever on shabbos? Whats the criteria? In general when can someone take a pain relever or medicine on shabbos?
It is pernitted to take a pain reliever if the headache is so severe that one would have to lay down to rest, or if one would not be able to function property. If the headache only causes discomfort, it would not be permitted to take pain relieving pills.
Sources: Shulchan Aruch and Mishnah Berurah 328; Shemiras Shabbos Kehilchasa Chap. 34.