Tums on Shabbos
Is one allowed to take tums chewable tablets on Shabbat/Yom Tov?
Tums are not actually a medicine, but rather a calcium supplement. When being used to maintain calcium intake and levels, i.e. as a nutritional supplement they may be taken on Shabbos.
When they are being taken to treat various ailments such as indigestion and heartburn, it would depend on the severity of the condition. If one is ill to the point where he is not functioning and bedridden, he may take medicine. If however one is suffering slight discomfort one may not take Tums as medicine.
See Igros Moshe O:C Vol. 3 Siman 54 Chapter 4