Psyllium (Metamucil, Fybogel, generics) – One teaspoonful of psyllium twice daily is often recommended for constipation, so why use it for diarrhea? The answer is that it has a water-holding effect in the intestines that may help bulk up watery stool. Some doctors recommend it for the variable bowel habit of IBS. It also has the ability to bind some toxins that may be the cause of acute diarrhea. Obviously, psyllium products combined with laxatives should be avoided.