Saccharomyces cerevisiae var. boulardii (strain CNCM I-745) · supplement
Evidence tier: moderate
A beneficial yeast that prevents and treats infectious diarrhoea, especially during and after antibiotics.
Partly established, unusually for this vault. S. boulardii is a live non pathogenic yeast that transits the gut without colonising it. It secretes a protease that degrades Clostridioides difficile toxin A and its receptor, and a phosphatase that inactivates endotoxin, and it competes with pathogens for adhesion sites and modulates mucosal immune signalling. Because it is a yeast, it is unaffected by antibacterial antibiotics, which is precisely why it can be co administered with them, and this is the one mechanistic claim in the batch that maps cleanly onto the clinical result.
Moderate, and this one earns it. Honesty cuts both ways and Saccharomyces boulardii has the best evidence in this batch. For preventing antibiotic associated diarrhoea, the systematic review with meta analysis by Szajewska and Kolodziej (2015, Alimentary Pharmacology and Therapeutics) pooled 21 randomised controlled trials: in children, 6 RCTs in 1,653 participants, incidence fell from 20.9 percent to 8.8 percent (RR 0.43, 95 percent CI 0.30 to 0.60); in adults, 15 RCTs in 3,114 participants, from 17.4 percent to 8.2 percent (RR 0.49, 95 percent CI 0.38 to 0.63). That is a consistent, replicated, decently powered effect on a hard clinical outcome, which is more than almost anything else in this vault can say. The Clostridioides difficile leg is weaker than the seed implies and has recently been downgraded: the 2025 Cochrane review of probiotics for preventing C. difficile associated diarrhoea (47 trials, 15,260 participants) reports only LOW certainty evidence, a relative risk reduction of about 50 percent but an absolute benefit of 1.6 percent and a number needed to treat of 65, downgraded for publication bias and low event rates. The 2017 Cochrane version had rated it moderate certainty; the update moved the other way. Note also that both Cochrane reviews assess probiotics as a class, not S. boulardii specifically. The IBS with diarrhoea indication in the seed is not supported by evidence of this quality and should not be carried at the same grade. Ceiling on the grade: the trials are strongest in a clinical setting (people on antibiotics, often inpatients), which is a treatment context, not a general wellness one.
Trials typically use 250 to 500 mg twice daily of the CNCM I-745 strain, roughly 5 to 20 billion CFU daily, started with the antibiotic course and continued for several days after it ends. Strain matters: the evidence attaches to S. boulardii CNCM I-745, not to yeast in general.
5 to 10 billion CFU daily, separately from antibiotics if applicable.
Avoid in central line catheters or severe immunocompromise (rare fungaemia risk).
Pregnancy: caution
Breastfeeding: caution
Active compounds: live Saccharomyces cerevisiae var. boulardii CNCM I-745 cells, secreted 54 kDa protease (degrades C. difficile toxin A), secreted phosphatase
Remedies using Saccharomyces Boulardii · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.