I first had vitagen when I was a teenager. Like your son I had a bad case of diarrhea and vomit. Since then I never take vitagen and dislike all artificial peach flavor taste. I took peach flavor that time. However, I do not have similar experience with yakult. I guess yakult is more tolerate than vitamin.Thanks Mummies. I think quite confirm is the vitagen. The bacteria is so powerful, he just had a round of diarrhea in his sleep, after stopping for 2 days. Sigh... Thought he had fully recovered. Never going to allow vitagen or yakult anymore!