Saccharomyces boulardii
Saccharomyces boulardii CNCM I-745
The probiotic yeast with the strongest evidence for preventing antibiotic-associated diarrhea
Evidence tier
Strong
Research weight
Citations
10 verified / 10
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.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| 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
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 ★ 10 studies
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.