boulardii

Saccharomyces boulardii is a non-pathogenic yeast used as a probiotic. It is commonly described as a strain of Saccharomyces cerevisiae, though some products market it as a separate species. Probiotic preparations typically label the strain as Saccharomyces boulardii CNCM I-745 or similar identifiers.

Medical use and evidence suggest Saccharomyces boulardii may help prevent antibiotic-associated diarrhea in adults and children and may reduce the duration of some forms of acute diarrhea, including traveler's diarrhea. The strength of the evidence varies by condition and population, with meta-analyses reporting modest benefits in some settings. It is generally not considered a substitute for standard medical treatment and should be used under professional advice, particularly in vulnerable individuals.

Mechanism of action is not fully understood. The yeast is thought to help maintain intestinal microbial balance, inhibit the growth or toxin production of certain pathogens, and modulate the host immune response. Some studies indicate S. boulardii can inactivate toxins produced by pathogens such as Clostridioides difficile and support intestinal barrier function, though these effects may be strain- and context-specific and are not universally observed.

Safety considerations: Saccharomyces boulardii is usually well tolerated, with common side effects including gas or abdominal discomfort. Rare but serious adverse events include fungemia or bloodstream infection, especially in severely ill or immunocompromised individuals or those with central venous catheters. Use is generally discouraged in these high-risk groups, and antifungal therapy may complicate its use. As with all probiotics, patients should consult healthcare providers to assess risks and appropriate dosing. Availability varies by country, and products are usually sold as dietary supplements with varying concentrations.