Saccharomyces boulardii

otherSaccharomyces cerevisiae metabolite

What is it

Saccharomyces boulardii is a beneficial yeast strain related to baker's yeast (S. cerevisiae) but with distinct properties. It is among the most extensively studied probiotic organisms and is widely used for prevention and treatment of various forms of diarrhea.

How it works

Saccharomyces boulardii is a non-pathogenic yeast that transiently colonizes the gut, exerting effects during its passage through the digestive tract. Because it is a yeast (eukaryote) rather than a bacterium, it is not affected by antibiotics, making it uniquely useful during antibiotic therapy when bacterial probiotics may be killed. It works through multiple mechanisms: it binds and neutralizes pathogenic toxins (notably C. difficile toxins A and B), inhibits pathogen attachment to intestinal cells, supports gut barrier function, modulates the immune system, and produces enzymes and proteins that aid digestion and intestinal health. Some research suggests it may also influence the underlying bacterial microbiome composition during recovery from disruption. Unlike many probiotic bacteria, S. boulardii has a body temperature optimum (37 deg C) at which it actively functions in the human gut. It does not permanently colonize and is cleared within days after stopping intake. The dose is measured in CFU or in milligrams (often interconvertible based on viability standards).

Evidence for 6 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Antibiotic-associated diarrhea prevention

Grade A

Strong evidence

Multiple RCTs and meta-analyses strongly support S. boulardii for preventing antibiotic-associated diarrhea in both adults and children. Effect sizes are clinically meaningful, with relative risk reductions of approximately 50%.

Acute infectious diarrhea (adults and children)

Grade A

Strong evidence

Strong evidence supports S. boulardii for reducing duration and severity of acute infectious diarrhea, including viral and bacterial causes.

Clostridioides difficile (C. diff) infection prevention

Grade B

Good evidence

S. boulardii reduces the risk of C. difficile infection during antibiotic therapy, particularly in high-risk patients. It is one of the few probiotics with specific evidence for C. diff prevention.

Traveler's diarrhea prevention

Grade B

Good evidence

Several trials suggest S. boulardii (250 to 1,000 mg per day) reduces the incidence of traveler's diarrhea when started before travel and continued during the trip.

H. pylori eradication (adjunct)

Grade B

Good evidence

When added to standard H. pylori treatment, S. boulardii may improve eradication rates and reduce side effects, including diarrhea from triple therapy.

Inflammatory bowel disease (IBD)

Grade C

Moderate evidence

Some small studies suggest S. boulardii may help maintain remission in Crohn's disease and ulcerative colitis. Evidence is limited; should be complementary, not primary therapy.

3 commercial forms

Saccharomyces boulardii CNCM I-745 (Florastor brand)

Most extensively studied strain in clinical research.

Used in many positive clinical trials. Considered the reference strain.

Generic S. boulardii capsules

Various strains; quality and viability vary.

Less expensive option. Look for products with verified CFU counts and reputable manufacturing.

S. boulardii powder (pediatric or feeding tube use)

Easily mixed into liquids; useful for children.

Commonly used in pediatric and clinical settings.

Dosage

Typical doses range from 250 mg to 500 mg taken 2 to 4 times daily during active diarrhea or antibiotic use, equivalent to 5 to 20 billion CFU per day. For prevention (during antibiotics or travel), 250 to 500 mg once or twice daily is common. Total daily doses up to 1,000 mg are well tolerated.

When and how to take it

WHEN: Take during antibiotic therapy and for several days after, or during periods of diarrhea risk (travel, gastroenteritis recovery). Can be taken any time of day. HOW: Take with water; can be combined with food. Because it is yeast, it survives stomach acid well and does not require enteric coating. Can be combined with antibiotic doses without separation, unlike bacterial probiotics.

Food sources

Food	Amount	%DV
Tropical fruits (lychee, mangosteen) — original isolation	N/A	—

Safety

Saccharomyces boulardii has an excellent safety profile in healthy people. Mild side effects include gas, bloating, and constipation. There is no established Tolerable Upper Intake Level. Serious adverse events (fungemia, fungal sepsis) are rare but have occurred in immunocompromised patients, those with central venous catheters, and critically ill patients, particularly when the yeast is inadvertently inhaled during product opening near catheter lines.

Who should be cautious

Immunocompromised individuals (HIV/AIDS, chemotherapy, transplant recipients, severe immunodeficiency) should not use S. boulardii due to risk of fungemia. People with central venous catheters or in critical care should avoid it (with rare exceptions under specialized medical supervision). Pregnant and breastfeeding women have less safety data; consult a clinician. People taking antifungal medications should not use this probiotic.

Interactions

Because S. boulardii is a yeast, antibiotics do not affect its viability, making it especially useful during antibiotic therapy. Antifungal medications (e.g., fluconazole, nystatin) can kill S. boulardii and should not be combined. Otherwise, few clinically significant drug interactions exist.

Frequently asked questions

Is S. boulardii a bacterium?⌄

No, it is a yeast. This is why it is not affected by antibiotics, unlike bacterial probiotics. It can be taken simultaneously with antibiotics.

Can I take it during antibiotic therapy?⌄

Yes. Unlike bacterial probiotics, S. boulardii is not killed by antibiotics. Start at the beginning of antibiotic therapy and continue for at least several days to a week after finishing antibiotics.

Is it safe for immunocompromised people?⌄

Generally no. Immunocompromised individuals, those with central venous catheters, and critically ill patients should avoid S. boulardii due to rare but serious risk of fungal infections.

What dose should I take?⌄

Typical adult doses are 250 to 500 mg one to four times daily. Higher doses are used during active diarrhea or antibiotic therapy; lower doses for prevention. Follow product directions.

How long can I take it?⌄

Short-term use (days to weeks) is well established. Longer-term use beyond a few months has less data but no specific safety concerns have emerged in healthy people.

References

Wikidata: Saccharomyces boulardii — Wikidata link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.