May a person take a caffeine tablet during their fast? The tablet would be placed under the tongue and dissolved without drinking any water so no food or water would be ingested.
Rav Shmuel Kanenetsky in קובץ הלכות ב/ח writes that for aches or pains, even if you are still obligated to fast, it is permissible to take pills on a fast day. One may even take a sip of water to get the pill down as well. [The exception would be Yom Kippur.]