One who suffers from mild sickness or ailments – that is, one who can walk around as though healthy, but experiences discomfort or irritation from a mild illness – has the same status as a healthy person. He must observe all the Shabbat and Yom Tov prohibitions, including the relatively minor rabbinic ones referred to as shvut di-shvut. However, if the illness or ailment causes pain, then any shvut di-shvut may be undertaken on his behalf. In other words, actions that are prohibited rabbinically may be done on his behalf, either by a non-Jew or by a Jew using a shinui. When it comes to these laws, the same rules apply to both Yom Tov and Shabbat (SA 307:5; MB 328:3; Peninei Halakha: Shabbat 9:11, 28:3).
However, when it comes to taking medicine, there is a difference between Shabbat and Yom Tov. The prohibition on taking medicine on Yom Tov is dependent upon the disagreement mentioned in the previous section. On Shabbat, the Sages prohibited taking medicine out of concern that one would end up grinding the ingredients, thus transgressing Toḥen. However, on Yom Tov, some are permissive, maintaining that just as black pepper may be ground up to season food, so too medicine may be ground up for someone who is sick. If grinding the medicine is permitted, taking it is certainly permitted. In contrast, according to the stringent view, the permissibility of doing melakha on Yom Tov applies to the needs of those who are healthy. It does not extend to the needs of the sick, since their needs are not shaveh le-khol nefesh. Accordingly, it is rabbinically prohibited to take medicine, out of concern that one will grind the ingredients. Nevertheless, the prohibition on taking medicine is rabbinic, and we are lenient in cases of doubt about rabbinic rules. Thus, we are lenient here, and medicine of all sorts may be taken on Yom Tov, whether liquids or pills. Similarly, a liquid medicine may be applied topically on Yom Tov.
. The prohibition on taking medicine is explained in Peninei Halakha: Shabbat 28:4-5. Many are stringent about this on Yom Tov too, since the Gemara forbids treating the eye on Yom Tov (Beitza 22a). This is the opinion of MA 532:2; Pri Megadim (Eshel Avrahamad loc. 2); Ḥayei Adam 103:1; MB 532:5; Kitzur Shulḥan Arukh 98:32; and SSK 34:1. Those who permit are the same authorities mentioned at the beginning of the previous footnote. We can add Ritva to their ranks (commentary to Beitza 22b). His reasoning is as follows: Since the entire prohibition of taking medicine on Shabbat is because of a concern that one will grind its ingredients and transgress Toḥen, this is not relevant to Yom Tov, when grinding black pepper is permitted. As for treating the eye, the prohibition is only because it is not clear that the treatment is effective. Aḥaronim present this approach as well, as detailed in Harḥavot. Since this is a case of doubt pertaining to a rabbinic law, we are lenient. Furthermore, some are of the opinion that even on Shabbat one may take modern, mass-produced medications, as there is no real concern that anyone will grind anything in order to produce the medicine. Although on Shabbat we rely on this leniency only if one is in pain (Peninei Halakha: Shabbat 28:5 n. 3) or if it is a medicine that must be taken for several days consecutively (28:6), on Yom Tov there are additional reasons to be lenient, so one may take medicine as needed. Moreover, even though melakhot that are permitted in the framework of okhel nefesh are otherwise prohibited by Torah law, if they are done by a non-Jew or using a shinui, they are prohibited only by rabbinic law. Since the poskim disagree as to whether melakhot permitted for okhel nefesh are also permitted for the sick, this is a case of doubt about a rabbinic law, and so we are lenient.