Daf Yomi is now dealing with medical treatments on Shabbat. The Mishnah on 109b gives a general principle:
משנה. אין אוכלין איזביון בשבת, לפי שאינו מאכל בריאים. אבל אוכל הוא את יועזר, ושותה אבוברואה. כל האוכלין אוכל אדם לרפואה וכל המשקין שותה, חוץ ממי דקלים וכוס עיקרין, מפני שהן לירוקה. אבל שותה הוא מי דקלים לצמאו, וסך שמן עיקרין שלא לרפואה.
The relevant part in English:
One may eat any food for healing purposes, or drink any liquid, except for palm tree water and root drink, which are for jaundice. But one may drink palm tree water for thirst, or apply root oil for purposes other than healing.
In other words, foods that are normally eaten by healthy people are exempt from the rabbinic decree against medicine on Shabbat, even when they eat those foods specifically for medicinal benefits. Foods that are normally eaten only for medicinal benefit may also be eaten by healthy people, but only if they don't specifically want the medicinal benefit.
A practical case today would be vitamins, which healthy people eat, but only for the health benefits.
How does this law view vitamins? Are they medicine? If so, are they prohibited to healthy people?
