Saccharomyces boulardii is a probiotic yeast that has been investigated for its role in managing gastrointestinal disorders, including Irritable Bowel Syndrome (IBS). The scientific support for its use in IBS is modest, with a rating of 2 out of 5 for evidence strength. Several randomized controlled trials and meta-analyses have evaluated probiotics in IBS, and some include S. boulardii either alone or in combination with other strains. A few small clinical trials suggest that S. boulardii may help reduce symptoms such as bloating, stool frequency irregularities, and abdominal discomfort, particularly in diarrhea-predominant IBS (IBS-D).

For example, a 2011 randomized, double-blind, placebo-controlled trial published in the World Journal of Gastroenterology found that S. boulardii led to a significant reduction in the number of daily stools and improved quality of life in IBS-D patients over a 4-week period. However, the sample sizes in these studies tend to be small, and results are sometimes inconsistent or only modestly positive. Meta-analyses examining probiotics in IBS typically find a small to moderate benefit, but S. boulardii-specific data are limited compared to multi-strain or bacterial probiotics.

In summary, there is emerging, but still limited, scientific evidence supporting the use of S. boulardii for IBS, particularly for diarrhea-predominant cases. More well-powered, high-quality trials are needed before it can be considered a mainstay therapy for IBS.