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.