Saccharomyces boulardii vs probiotics: what's the difference?
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
S. boulardii is a yeast, not a bacterium — which means antibiotics do not kill it. That single difference makes it the best-evidenced option for antibiotic-associated diarrhoea, where bacterial probiotics have to be spaced around doses and are killed anyway.
Key takeaways
- It is a yeast, so antibacterial antibiotics have no effect on it.
- Multiple meta-analyses support it for antibiotic-associated diarrhoea.
- Fungaemia has been reported in critically ill and immunocompromised patients — a firm contraindication.
The key difference
Saccharomyces boulardii is a tropical yeast, related to brewer's yeast, isolated from lychee in the 1920s. Because antibiotics target bacterial machinery, they leave yeast untouched. Bacterial probiotics taken alongside antibiotics are partly destroyed, which is why the usual advice is to space doses by several hours — advice that becomes unnecessary with S. boulardii.
What it is used for
Meta-analyses support it for preventing antibiotic-associated diarrhoea, and it has evidence in traveller's diarrhoea, acute infectious diarrhoea in children, prevention of C. difficile recurrence, and as an adjunct during H. pylori eradication. It works partly by producing a protease that degrades C. difficile toxins A and B, and partly by competing with pathogens for adhesion sites. Like bacterial probiotics it is transient and clears within days of stopping.
The safety exception
In generally healthy people it is well tolerated. But fungaemia — bloodstream infection with the yeast — has been documented in critically ill patients, immunocompromised patients and people with central venous catheters, including cases where capsules were opened near a line. This is a firm contraindication rather than a cautious footnote.
Key ingredients to understand
The ingredients most relevant to this question, with what the evidence actually supports:
- Saccharomyces boulardii — 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…
- Probiotics (Lactobacillus & friends) — Probiotics are live microorganisms that can support digestion — but their effects are strain-specific, so the exact strains and dose matter more…
- Bacillus coagulans — B. coagulans is a spore-forming probiotic, which means it survives stomach acid, heat and years on a shelf without refrigeration. That practical…
- Inulin (Prebiotic Fibre) — Inulin is a prebiotic soluble fibre (from chicory root) that feeds beneficial gut bacteria, supports regularity and calcium absorption, and adds…
Frequently asked questions
What dose and when?
250–500 mg (roughly 5–10 billion CFU) twice daily, started with the antibiotic and continued for one to two weeks after finishing.
Can I take it with antifungal medication?
No — antifungals will inactivate it. That is the one drug class that matters here.
Is it better than bacterial probiotics generally?
For antibiotic-associated diarrhoea, it has among the strongest evidence available. For general gut health, bacterial strains are better studied.
Related on FactoWiki
- Gut & Digestive Health supplements — the full category
- All health answers
- Ingredient evidence guides
- Saccharomyces boulardii — ingredient guide
- Probiotics (Lactobacillus & friends) — ingredient guide
- How we review
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