Do "Tums" and "Pepto Bismol" cause the food in your subject to not be absorbed?

If you take a lot, then yes.. it does. They are both based on Calcium Carbonate (tums) and Bismuth subsalicylate (Pepto Bismol) messes with natural digestion. Both, if taken obsessively and overly, interrupt with the regular absorption of nutrients.

If you take enough for them to interfere with absorption you probably have bigger things to worry about.

@Lightlyseared exactly.

It inhibits the absorption of the nutrients. One of the ironies of putting calcium and D in milk. Milk calms the stomach acids resulting in lower absorption. I think now they add vitamins to orange juice, which increases absorption, but orange juice is very high in sugar.

As above comments but add cut down you intake of milk.