NutriDex

The Supplement Research Compendium
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Saccharomyces boulardii

Saccharomyces boulardii CNCM I-745

The probiotic yeast with the strongest evidence for preventing antibiotic-associated diarrhea

Strong evidence 🦠Probiotics🛡️Gut & Immune

✚ Updated · How we grade evidence

Evidence tier
Strong
Research weight
Citations
14 verified / 14
Classification
Probiotics
❝
What the evidence says. Multiple high-quality RCTs / meta-analyses with consistent effects.

What is Saccharomyces boulardii?

Saccharomyces boulardii (Saccharomyces boulardii CNCM I-745) is a probiotic strain used for prevents antibiotic-associated diarrhea in adults and children (~50% relative risk reduction; nnt ~10). NutriDex grades the human evidence as Strong. Saccharomyces boulardii CNCM I-745 is a non-pathogenic probiotic yeast (intrinsically resistant to antibacterial antibiotics) with its best-supported indication being prevention of antibiotic-associated diarrhea (AAD): pooled meta-analyses of RCTs show roughly a 50% relative risk reduction (RR ~0.47, 95% CI 0.35-0.63), with a number-needed-to-treat near 10. It also shortens acute infectious/pediatric gastroenteritis by about 1 day and, as an adjunct, improves H. pylori eradication tolerability by cutting therapy-related diarrhea and nausea. Evidence for Clostridioides difficile infection prevention and for IBS is more limited and mixed. It is generally well tolerated, but carries a rare but real fungemia risk that contraindicates use in critically ill, immunocompromised, or central-venous-catheter patients.

Purported Benefits

✓Prevents antibiotic-associated diarrhea in adults and children (~50% relative risk reduction; NNT ~10)
✓Reduces the duration of acute infectious diarrhea / pediatric gastroenteritis by roughly 1 day and shortens hospital/ER stay
✓Used as an adjunct, improves tolerability of H. pylori eradication therapy (fewer total adverse events, less diarrhea and nausea) and modestly raises eradication rates
✓Helps prevent traveler's diarrhea in adults (guideline-level recommendation)
✓May improve disease-specific quality of life in IBS, though effects on individual symptoms are inconsistent
✓Antibiotic-resistant yeast, so it can be co-administered with antibacterial therapy without being killed

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Prevention of antibiotic-associated diarrheaMultiple large meta-analyses show ~50% relative risk reduction (RR ~0.47), NNT ~10. Strong ↑ benefit · moderate 3
Acute infectious/pediatric diarrhea durationMeta-analyses show ~1-1.6 day shorter diarrhea and improved cure rates in children. Strong ↑ benefit · moderate 2
H. pylori eradication therapy tolerabilityMeta-analysis: fewer total adverse events (~18% vs 35%) and modestly higher eradication as adjunct. Moderate ↑ benefit · moderate 1
C. difficile infection preventionOne meta-analysis (RR 0.30) and an RCT suggest reduced recurrence; evidence limited and mixed. Preliminary ↑ benefit · moderate 2
IBS symptomsOne RCT improved IBS quality of life but not individual symptoms; inconsistent. Preliminary ↔ mixed · small 1

Dosing & Compounds

Typical Dose
Typical trial dosing is about 5-10 billion CFU/day (roughly 250-500 mg lyophilized yeast/day, often split BID); for AAD prevention, start within 1-2 days of beginning antibiotics and continue through the antibiotic course plus a few days after. It can be taken at the same time as antibacterial antibiotics since the yeast is intrinsically resistant.
Active Compounds
Saccharomyces boulardii CNCM I-745 (= S. cerevisiae var. boulardii)Branded: Florastor (US), Ultra-Levure / Perenterol / Florastor (EU)Lyophilized (freeze-dried) capsules, sachets, and powderCommon strengths of 250 mg or 5 billion CFU per capsule/sachet

Safety & Cautions

Generally well tolerated in immunocompetent patients; the main concern is fungemia (yeast bloodstream infection). Cumulative pharmacovigilance reported dozens of fungemia cases with several fatalities, mostly in critically ill or immunocompromised patients and those with central venous catheters (capsule opening can aerosolize spores onto catheter sites). The EMA (2017) concluded the benefit-risk is unfavorable in critically ill or immunocompromised patients. AVOID in critically ill, immunocompromised, or central-line patients; handle/open capsules away from catheters. Use caution with concurrent systemic antifungals (may reduce efficacy) and in pregnancy/yeast allergy. Educational only — always check with your doctor or pharmacist before combining Saccharomyces boulardii with any medicine.

Key Studies ★ 14 studies

Systematic review Westphal 2026 ✓ PubMed
Meta-analysis of Saccharomyces boulardii as an add-on to Helicobacter pylori eradication therapy.
Systematic review Dong 2026 ✓ PubMed
Saccharomyces boulardii as a probiotic yeast in food applications and its health properties: a review and future perspectives
systematic review / meta-analysis Frontiers (Pediatric acute diarrhea, China) 2025 ✓ Full text
Meta-analysis of Chinese RCTs found S. boulardii CNCM I-745 reduced duration of pediatric acute diarrhea by ~1.63 days (95% CI -2.08 to -1.18) and improved cure rates.
systematic review / meta-analysis McFarland & Li (China AAD/CDI) 2024 ✓ Source
Meta-analysis (46 trials, 8,201 participants): CNCM I-745 reduced AAD (RR 0.43, 95% CI 0.40-0.48) and C. difficile infection (RR 0.30, 95% CI 0.10-0.87).
systematic review / meta-analysis H. pylori adjuvant meta-analysis 2024 ✓ Source
Adding S. boulardii to eradication therapy lowered total adverse events (~18% vs ~35% control) and reduced diarrhea, nausea, and bloating while modestly improving eradication.
meta-analysis Szajewska & Kołodziej 2015 ✓ PubMed
Meta-analysis (21 RCTs, n=4780): S. boulardii reduced antibiotic-associated diarrhea risk vs control (RR 0.47, 95% CI 0.38-0.57).
systematic review / meta-analysis McFarland 2010 ✓ PubMed
Systematic review/meta-analysis in adults: S. boulardii significantly protective for AAD (pooled RR 0.47, 95% CI 0.35-0.63) and supported for traveler's diarrhea.
RCT Chitapanarux 2025 ✓ Source
In 120 CDI patients, adding S. boulardii (250 mg twice daily) to vancomycin produced similar clinical cure (98.4% vs 98.3%) but a higher global cure rate and reduced recurrence without increasing adverse events.
RCT Preechakawin 2025 ✓ Full text
In a three-arm RCT of severely ill patients with non-C. difficile nosocomial diarrhea, adjunctive S. boulardii (and bismuth subsalicylate) added no benefit over standard care across stool frequency, consistency, and other outcomes.
RCT BMC Gastroenterol 2023 ✓ Source
Single-centre RCT in adults found S. boulardii CNCM I-745 effective in acute inflammatory viral diarrhoea compared with control.
randomized controlled trial Choi et al. 2011 ✓ PubMed
RCT in IBS (n=67): S. boulardii improved IBS quality-of-life vs placebo (15.4% vs 7.0% improvement, P<0.05), without superiority for individual symptoms.
safety review / case series Rannikko et al. (CDC EID) 2021 ✓ Source
Review of fungemia and fungal infections linked to S. boulardii supplements, predominantly in ICU/immunocompromised patients and those with central venous catheters.
Review Balboa 2026 ✓ PubMed
Clinical algorithm for probiotic use in preventing antibiotic-associated diarrhea in adults and children.
Review Żywczak 2026 ✓ PubMed
Review spanning yeast probiotics to postbiotics, with a yeast-specific functional perspective.
14 sources cited · 14 verified Search all studies on PubMed ↗

Common questions about Saccharomyces boulardii

What is Saccharomyces boulardii used for?

Saccharomyces boulardii is most often taken for Prevents antibiotic-associated diarrhea in adults and children (~50% relative risk reduction; NNT ~10), Reduces the duration of acute infectious diarrhea / pediatric gastroenteritis by roughly 1 day and shortens hospital/ER stay, Used as an adjunct, improves tolerability of H. pylori eradication therapy (fewer total adverse events, less diarrhea and nausea) and modestly raises eradication rates, Helps prevent traveler's diarrhea in adults (guideline-level recommendation). The probiotic yeast with the strongest evidence for preventing antibiotic-associated diarrhea

Does Saccharomyces boulardii work — what does the evidence say?

Strong evidence. Multiple high-quality RCTs / meta-analyses with consistent effects. Saccharomyces boulardii CNCM I-745 is a non-pathogenic probiotic yeast (intrinsically resistant to antibacterial antibiotics) with its best-supported indication being prevention of antibiotic-associated diarrhea (AAD): pooled meta-analyses of RCTs show roughly a 50% relative risk reduction (RR ~0.47, 95% CI 0.35-0.63), with a number-needed-to-treat near 10. It also shortens acute infectious/pediatric gastroenteritis by about 1 day and, as an adjunct, improves H. pylori eradication tolerability by cutting therapy-related diarrhea and nausea. Evidence for Clostridioides difficile infection prevention and for IBS is more limited and mixed. It is generally well tolerated, but carries a rare but real fungemia risk that contraindicates use in critically ill, immunocompromised, or central-venous-catheter patients.

What is the typical dose of Saccharomyces boulardii?

Typical trial dosing is about 5-10 billion CFU/day (roughly 250-500 mg lyophilized yeast/day, often split BID); for AAD prevention, start within 1-2 days of beginning antibiotics and continue through the antibiotic course plus a few days after. It can be taken at the same time as antibacterial antibiotics since the yeast is intrinsically resistant.

Is Saccharomyces boulardii safe? Any cautions or side effects?

Generally well tolerated in immunocompetent patients; the main concern is fungemia (yeast bloodstream infection). Cumulative pharmacovigilance reported dozens of fungemia cases with several fatalities, mostly in critically ill or immunocompromised patients and those with central venous catheters (capsule opening can aerosolize spores onto catheter sites). The EMA (2017) concluded the benefit-risk is unfavorable in critically ill or immunocompromised patients. AVOID in critically ill, immunocompromised, or central-line patients; handle/open capsules away from catheters. Use caution with concurrent systemic antifungals (may reduce efficacy) and in pregnancy/yeast allergy.

How many studies support Saccharomyces boulardii?

NutriDex cites 14 sources for Saccharomyces boulardii, graded "Strong".

Cite this page
APA

Peh, D. (2026). Saccharomyces boulardii (Saccharomyces boulardii CNCM I-745): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 16 Sept 2026, from https://nutridex.info/s/s-boulardii

BibTeX
@misc{nutridex_s_boulardii,
  author       = {Peh, Daryl},
  title        = {Saccharomyces boulardii (Saccharomyces boulardii CNCM I-745): Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/s-boulardii},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-09-16}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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