May one take medicine on Yom Kippur?
One who is currently sick: If one is bedridden, or feels ill/weak in his entire body, then he may swallow a tasteless or bitter pill [without water, as will be explained]. If the pill has a non-bitter taste, then he is to wrap it in precut tissue [as one may not cut it on Shabbos or Yom Kippur] and swallow it with the tissue. This allowance applies even if the illness does not involve danger. If, however, one is not bedridden, and does not feel ill in his entire body, then he may not take medication, even if he is in pain or is suffering from a headache and the like.
One who is not currently sick but suffers from a medical condition: Those who are not sick but suffer from a medical condition which requires a daily dose of medication, are to verify with their doctor if they can fast, and skip the dose on Yom Kippur, without any health risks involved. In the event that the doctor states that skipping the medicine can lead to medical complications that can lead to a life-threatening situation, then he must take the pill even on Yom Kippur. If swallowing the pill in one of the above-mentioned methods is not possible, one may swallow it with water. [Likewise, if skipping a dose can lead to illness, even non-life threatening, then one may take it on Yom Kippur, although without water, as explained below.]
How to take the pill: One who is permitted to take a pill on Yom Kippur, as stated above, must swallow the pill plain, without water, and if the pill has a non-bitter taste, he is to swallow it in a precut piece of tissue. He may not swallow the pill with water, unless the illness poses a danger of life and he cannot manage to swallow it without the water. Alternatively, some Poskim suggest that before Yom Kippur, one can crush the bitter pill into powder, add it to the water, and then drink the bitter mixture. This applies even if one illness does not pose any danger of life.
 Sdei Chemed Yom Kippur 3:8; Yeshuos Yaakov 612; Kesav Sofer 111; Pischeiy Teshuvah Y.D. 155:6; Shoel Umeishiv Mahdura Daled 1:55; Orchos Chaim 618:1; Eretz Tzevi 88; Kaf Hachaim 554:34 in name of in name of Kesonos Yosef 4, Ikarei Hadaat 29:36, Pischei Olam 554:6 regarding regular fast days; Meishiv Shalom 179; Igros Moshe 3:91; Tzitz Eliezer 10:25; Shevet Halevi 10:89; SSH”K 39:8; Nishmas Avraham 612:7; Toras Hayoledes 52:9 footnote 27; Piskeiy Teshuvos 612:2; Nitei Gavriel 37:23; 39:12-15; Encyclopedia Hilchatit Refuit Erech Yom Kippur Volume 3 p. 794
See regarding the status of the prohibition of consuming inedible items on Yom Kippur: Admur 612:8 and Michaber 612:6 based on Rambam that it is forbidden; Tur 612 in name of Avi Ezri [i.e. Ravayah] that there is no even rabbinical prohibition involved; Beis Yosef 612 that possibly there is no prohibition even according to Rambam if less than the Shiur; Meishiv Shalom 179 that according to the final ruling of the Michaber [and Admur] who omitted all the above leniency’s, one is to be stringent even by less than the Shiur; Shevet Halevi 10:89 that one who is lenient for the sake of a mitzvah is not to be protested;
 Poskim ibid
The reason: One who is bedridden, or weak in his entire body has the Halachic definition of a Choleh Sheiyn Bo Sakana, of which we rule that the Rabbinical prohibitions against taking medicine on Shabbos, and against eating Rabbinical prohibited foods, is lifted. Thus, being that swallowing a bitter pill is only Rabbinically forbidden on Yom Kippur, as it is not a food, and is not being eaten in the normal method, it therefore may be swallowed by an ill person. [ibid]
 Rav SZ”A in SSH”K ibid; Nishmas Avraham ibid; Piskeiy Teshuvos ibid
 Piskeiy Teshuvos ibid; Nitei Gavriel ibid
The reason: This is due to two prohibitions 1) The prohibition against eating, which Rabbinically includes even bitter and inedible foods. 2) The prohibition against taking medication on Shabbos and Yom Kippur.
 Igros Moshe ibid based on ruling of Rav Akiva Eiger
The reason: As we view a potential life-threatening illness that can come as a result of not eating, or not taking medicine, as a life-threatening situation, for which one can break his fast on Yom Kippur. [ibid]
 Igros Moshe ibid
 Nishmas Avraham O.C. 612:7; Encyclopedia Hilchatit Refuit Erech Yom Kippur Volume 3 p. 795
 Igros Moshe ibid; SSH”K ibid; Nishmas Avraham ibid; Piskeiy Teshuvos ibid
 Kaf Hachaim 554:34 in name of Poskim regarding Tisha B’av; Heard from Rav Yaakov Yosef that the same applies on Yom Kippur, and so seems Pashut; Nishmas Avraham 5 612:2; SSH”K ibid; Piskeiy Teshuvos ibid; Nitei Gavriel ibid; Encyclopedia Hilchatit Refuit Erech Yom Kippur Volume 3 p. 795 footnotes 340-343