Candida albicans is a fungus that naturally grows in the human body, but if its numbers become too large it can cause gastrointestinal infections. Saccharomyces boulardii was tested for its ability to counterbalance Candida albicans and was found to diminish the activity of the harmful fungus.

The ability of Saccharomyces boulardii to reduce antibiotic-associated diarrhea (AAD) was tested in a human double-blind, placebo-controlled study in 1995. In the group receiving Saccharomyces boulardii, 7 of 97 (7.2%) of the patients experienced diarrhea, whereas 14 of 96 (14.6%) of the placebo group experienced diarrhea.