Saccharomyces Boulardii

The verdict

Is Saccharomyces Boulardii worth taking?

Saccharomyces boulardii is in a category of its own as a probiotic: it is a yeast rather than a bacterium, making it the only probiotic inherently resistant to every antibiotic currently in clinical use. This makes it uniquely valuable during antibiotic courses when all bacterial probiotics are being killed alongside the target pathogens. Take it simultaneously with antibiotics without the typical separation timing that bacterial probiotics require. CNCM I-745 is the most clinically studied strain. 250 to 500 mg twice daily is the dose with the strongest evidence across all its applications.

What it does

What Saccharomyces Boulardii does in the body

Antibiotic-associated diarrhea prevention, C. difficile infection and recurrence reduction, traveler’s diarrhea prevention, and gut microbiome resilience during and after antibiotic treatment. Saccharomyces boulardii is a tropical yeast probiotic that occupies a unique position in the probiotic landscape: being a fungus rather than a bacterium, it is completely unaffected by antibacterial antibiotics and can colonize the gut and confer protective effects during antibiotic courses when all bacterial probiotics are simultaneously being eliminated. It also demonstrates activity against pathogenic bacteria through competitive exclusion, toxin binding, and immune modulation, all without establishing permanent colonization since it clears within 3 to 5 days of stopping supplementation.

The evidence

What the research actually shows

Strong for antibiotic-associated diarrhea prevention specifically, one of the most replicated findings in the clinical probiotic literature. A 2024 meta-analysis confirmed 250 to 500 mg twice daily in a dose-dependent manner for antibiotic-associated diarrhea prevention. A 2026 narrative review in Microorganisms confirmed safety and efficacy across both pediatric and adult populations for diarrheal conditions broadly. Evidence for C. difficile recurrence reduction is also strong, with multiple randomized controlled trials showing significant reduction in recurrence rates.

Food first

Getting Saccharomyces Boulardii from food

Saccharomyces boulardii is not present in commonly available fermented foods. Some traditional fermented beverages contain related Saccharomyces yeasts but not the specific CNCM I-745 strain. Supplementation is the only practical route to the therapeutic applications discussed above, particularly during antibiotic courses where the antibiotic-resistance property is the defining clinical advantage.

What the guide adds

The part that is not on this page

Everything above is the assessment. What the guide adds for Saccharomyces Boulardii is the protocol:

• Optimal Form
• Bioavailability
• Purity Red Flags
• Stack With / Avoid

147 entries across nine categories, every one graded against the clinical literature the same way.

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About the author

Who graded this

Daniel Edlund is a Le Cordon Bleu-trained private chef in Los Angeles, a certified personal trainer and strength coach, and an internationally licensed massage therapist. Thirty years of strength training and fifteen years cooking in private estate kitchens. He is the author of The Complete Supplement Guide, which grades 147 entries against the clinical literature, and of The EASY Way to Organic Cooking, first published in 2013.

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This page is information, not medical advice. Supplements interact with prescription medication and with each other, and the right answer depends on your own bloodwork and history. Talk to your doctor before starting anything, particularly if you are pregnant, nursing, managing a health condition, or already taking medication.

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All 147 entries, graded →