To increase your tolerance of vitamin c, use sodium buffered powder, multi- mineral buffered powder, but stay away from calcium ascorbate and straight acidic vitamin c powder.
Alway take vitamin c after meals, always sip it and do not chug it.
Tums with c is great idea! 1,000 mg calclium carbonate.
Also, timed release should be part of your regime....by taking half of your c by timed- release and buffered, you will not experience the GI upset you get.
But if you are taking it for current diagnosis of cancer, please know that there is good likely hood the action is prooxidant and therefore, why not just focus on the active ingredient,....oxygen! Vitamin c has other anti cancer properties other than pro oxidant, and still can be part of an ozone protocol. Ozone is pure, molecular oxygen that is slightly less reactive than singlet oxygen and other reactive oxygen species