The Sages further enacted that one who is bothered by an ailment or mild illness may not obtain medical treatment on Shabbat. That is, he may not ingest medicine, apply a medicinal ointment, or take any actions designed for the purpose of healing. The concern is that one who is preoccupied with alleviating the ailment will pulverize herbal ingredients to prepare a medication and thereby violate the Torah prohibition of Toĥen (Shabbat 54b and Rashi).
Thus, the Sages forbade someone with an eye ailment to drip wine or another medication to his eye (SA 328:20). Similarly, one may not apply ointment to a wound to heal it (SA 328:22). If one has a sore throat, he may not gargle with oil for therapeutic purposes. One who has a toothache may not rinse his teeth and gums with vinegar, salt water, or alcohol for therapeutic purposes. However, he may drink an alcoholic beverage in order to relieve the pain, on condition that he does not retain the liquid in his mouth longer than usual (SA 328:32).
If the ailment causes pain, one may ask a non-Jew to drip wine to his eye or apply alcohol to his painful tooth. This reduces the prohibition to the level of shvut di-shvut, which the Sages permitted if one is in pain (SA 307:5; 328:25; above, 9:11-12 and Harĥavot; according to Radbaz and R. Mordechai Benet, a Jew in pain may take medicine by himself; see n. 3 below).
The enactment prohibiting taking medicine also includes eating or drinking items that only sick people eat or drink. However, a sick person may eat or drink items that healthy people eat or drink as well, even if his intention is to use these items as medicine (Shabbat 109b; SA 328:37). Therefore, one who has a sore throat may not suck on throat lozenges, but he may suck on ordinary hard candies (SSK 34:4). Similarly, one may not drink water with flaxseed to ease constipation, but prune juice is permitted, as healthy people sometimes drink it as well.
One who experiences discomfort may do things that healthy people normally do, even if his intention is to relieve the discomfort. For example, one who has itchy skin may apply oil that healthy people apply as well (SA 327:1). One may also apply oil to one’s hands and lips, since nowadays people do so even when their skin is not chapped – to soften them or for pleasure.
If one has medicine that helps relieve his minor aches and pains, he may mix it into a drink before Shabbat, as long as no one can tell that it contains medicine. He may then drink the medicinal liquid on Shabbat (R. Shlomo Zalman Auerbach, cited in SSK 34:5).