Saccharomyces boulardii: Uses, Benefits, Dosage & Safety
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Quick summary
S. boulardii is a probiotic yeast, not a bacterium — which is why antibiotics do not kill it. It has some of the strongest evidence in the whole probiotic field, particularly for antibiotic-associated diarrhoea and traveller's diarrhoea, backed by multiple meta-analyses.
What is Saccharomyces boulardii?
Saccharomyces boulardii is a tropical yeast, a strain of S. cerevisiae var. boulardii, isolated from lychee and mangosteen in the 1920s. Because it is a yeast rather than a bacterium, antibiotics do not affect it — the single most useful practical feature it has.
What Saccharomyces boulardii is commonly used for
Antibiotic-associated diarrhoea, traveller's diarrhoea, Clostridioides difficile recurrence prevention, acute infectious diarrhoea in children, and adjunctive use in H. pylori eradication.
How Saccharomyces boulardii works
It works through several routes: producing a protease that degrades C. difficile toxins A and B, competing with pathogens for adhesion sites, supporting the intestinal barrier, and modulating local immune signalling. It does not colonise the gut permanently — it clears within days of stopping.
What the evidence says
Each claim below is tied to the specific study behind it, rather than to a general reading list.
- Meta-analysis of randomised trials found S. boulardii significantly reduced the risk of antibiotic-associated diarrhoea. Szajewska & Kolodziej, Alimentary Pharmacology & Therapeutics, 2015 — systematic review and meta-analysis. (PubMed)
- S. boulardii produces a protease that degrades C. difficile toxin A. Castagliuolo et al., Infection and Immunity, 1996 — mechanistic study. (PubMed)
- Fungaemia has been reported in critically ill and immunocompromised patients. Enache-Angoulvant & Hennequin, Clinical Infectious Diseases, 2005 — review of reported cases. (PubMed)
Typical dosage used in studies
250–500 mg (roughly 5–10 billion CFU) twice daily is the range used in most trials. For antibiotic-associated diarrhoea it is typically started with the antibiotic and continued for a week or two after finishing.
Side effects and safety
Well tolerated in the general population. The important exception is serious: fungaemia — bloodstream infection with the yeast — has been documented in critically ill patients, immunocompromised patients and people with central venous catheters. Capsules should not be opened near a catheter line.
Medication interactions and who should avoid Saccharomyces boulardii
Medication & safety check
Antifungal medications will inactivate it, so the two should not be combined. It is not affected by antibiotics, which is the point of using it alongside them.
General information, not personal medical advice. If you take any medication, confirm it is safe to combine with Saccharomyces boulardii with your doctor or pharmacist first.
Sources & further reading
The claim-level citations above are drawn from these sources:
- Szajewska & Kolodziej, Alimentary Pharmacology & Therapeutics, 2015 — systematic review and meta-analysis — find on PubMed
- Castagliuolo et al., Infection and Immunity, 1996 — mechanistic study — find on PubMed
- Enache-Angoulvant & Hennequin, Clinical Infectious Diseases, 2005 — review of reported cases — find on PubMed
- NIH Office of Dietary Supplements
- NIH National Center for Complementary and Integrative Health
Frequently asked questions
Can I take it at the same time as antibiotics?
Yes — and that is the main reason to choose it. As a yeast it is unaffected by antibacterial drugs, unlike Lactobacillus or Bifidobacterium probiotics, which need to be spaced apart from doses.
Who should not take it?
Anyone who is immunocompromised, critically ill, or has a central venous line. Documented cases of bloodstream infection make this a firm contraindication rather than a cautious note.
Is it better than bacterial probiotics?
For antibiotic-associated diarrhoea specifically, it has among the strongest evidence available. For general gut health, bacterial strains are better studied.
Where you'll find Saccharomyces boulardii
Saccharomyces boulardii appears in Gut & Probiotics formulas. Browse the supplement guides to see the products we review, each with a full breakdown of formula, pricing and safety.
Related ingredients to explore
Ingredients often studied or formulated alongside Saccharomyces boulardii.
General information, not medical advice.