Supplement
Saccharomyces boulardii
Saccharomyces boulardii is a probiotic yeast taken by mouth, mostly alongside antibiotics. A 2015 meta-analysis of 21 trials found diarrhoea during antibiotic courses fell to 8.5% from 18.7% in children and adults, yet a 477-patient trial in German hospitals was stopped early with no benefit. Added to H. pylori treatment, it raised clearance slightly and roughly halved treatment-related diarrhoea in pooled trials. In children with acute gastroenteritis it shortened diarrhoea by about a day, on very low-quality evidence. It did not clearly prevent C. difficile diarrhoea in adults or relapse of Crohn's disease. Its main risk is a rare bloodstream yeast infection, mostly in people who are critically ill, fed by tube or drip, or have a central line.
Sources: PMID 26216624; PMID 26973849; PMID 25898944; PMID 42764401; PMID 32056266; PMID 23466709; PMID 36806741; PMID 34287140
- Updated
- How we grade
- 41 studies cited
- Best evidence
- Grade A: strong evidence
What the evidence says
- Antibiotic-associated diarrhoea: pooling 21 randomized trials with 4,780 people, a 2015 meta-analysis found that 8.5% of those taking S. boulardii got diarrhoea against 18.7% on placebo or no treatment (risk ratio 0.47; number needed to treat 10); in children the figures were 8.8% against 20.9% (6 trials) and in adults 8.2% against 17.4% (15 trials). A 2010 analysis of adult trials gave the same risk ratio. Single trials differ. It halved diarrhoea in 193 hospital patients on beta-lactam antibiotics (7.2% against 14.6%), lowered it from 9% to 1.4% in 151 inpatients, and in a 2026 trial in 100 inpatients 7.8% had diarrhoea against 71.4% on placebo. But in 15 German hospitals, 250 mg twice a day from the start of antibiotics until a week after them made no difference in 477 adults with mean ages of 56.5 and 60.1 (21 against 19 cases), and the trial was stopped early for futility; in 275 inpatients aged 79.2 on average it did not prevent diarrhoea either (15.1% against 13.3%). A 2019 Cochrane review of 33 probiotic trials in children found a moderate protective effect and said the benefit of high-dose products such as S. boulardii still needs a large, well-designed trial; a 2024 Chinese trial in infants and young children found less diarrhoea with S. boulardii than in controls given no probiotic.
- C. difficile: in the 2015 meta-analysis, C. difficile diarrhoea fell significantly only in the 2 trials in children (579 children; risk ratio 0.25); across 9 adult trials with 1,441 people the risk ratio of 0.8 left room for no effect. As an add-on for people already being treated, a 1994 trial in 124 adults found that 1 g a day for 4 weeks with standard antibiotics cut recurrences in those who had relapsed before (34.6% against 64.7%) but not after a first episode; a 2000 trial found fewer recurrences only alongside high-dose vancomycin; and in a 2025 trial of 120 patients with mild to moderate infection, clinical response matched placebo while recurrences fell (1.7% against 13.1%). The 2025 Cochrane review of all probiotics, on low-certainty evidence, estimated that 65 people need to take them to prevent one case, and a 2026 American Gastroenterological Association expert review does not advise probiotics to prevent a first or repeat infection.
- H. pylori: added to antibiotic treatment, not instead of it, S. boulardii raised eradication from 71% to 80% in a 2015 meta-analysis of 11 trials (2,200 people, 330 of them children; moderate-quality evidence) and cut treatment-related diarrhoea (risk ratio 0.51, high-quality evidence) and nausea. A 2026 meta-analysis of 19 trials found smaller gains in adults (risk ratio 1.07, about 18 treated for one more person cleared) than in children (1.12), with moderate certainty, and adverse events fell from 36.0% to 19.7%; a 2023 analysis of 15 trials in children found eradication of 87.7% against 75.9%. With bismuth quadruple therapy the gain was small: across 6 trials (1,404 patients) eradication went from 83.3% to 87.0%, not significant per protocol, while diarrhoea fell from 25.7% to 7.9%. Taken alone without antibiotics, it cleared the infection in 6 of 63 people.
- Acute diarrhoea and travel: for children with acute gastroenteritis, the 2020 update of an S. boulardii meta-analysis (29 trials) pooled 23 of them: diarrhoea ended 1.06 days sooner and hospital stays were 0.85 days shorter than with placebo or nothing, though only one trial was fully blinded and the evidence was judged very low quality. A Bayesian network analysis in 2021 put it at or near the top of the probiotics compared, with moderate evidence, and an umbrella review in 2026 (36 meta-analyses) stressed that effects depend on the strain. A 2020 Cochrane review of all probiotics for acute infectious diarrhoea found no benefit in its low-risk-of-bias trials (risk ratio 1.00), but those trials tested bacterial probiotics, not S. boulardii; in its S. boulardii subgroup, diarrhoea lasting 2 days or more was not significantly less common (risk ratio 0.70, 9 trials, results varying widely), while diarrhoea lasted about 24.6 hours less (11 trials). For travellers, a 2019 meta-analysis found one S. boulardii strain lowered traveller's diarrhoea (risk ratio 0.79), while the other probiotics tested did not reach significance, and 2007 and 2024 analyses also listed S. boulardii among the strains that prevented it.
- Other uses: in 165 people with Crohn's disease in remission, a year of S. boulardii did not prevent relapse (47.5% against 53.2% on placebo). In irritable bowel syndrome it improved quality of life more than placebo but not individual symptoms in 67 patients over 4 weeks; a 2021 strain-specific meta-analysis found more abdominal pain relief (risk ratio 1.5), while a 2026 one called its results conflicting. In 128 critically ill tube-fed patients it reduced the share of feeding days with diarrhoea from 18.9% to 14.2%, and in an open-label trial in severe acute pancreatitis, hospital infections occurred in 0 of 27 patients against 5 of 23. In preterm infants, a 2021 meta-analysis of 10 trials (1,264 infants) found less necrotising enterocolitis (risk ratio 0.56) and feeding intolerance, but no change in sepsis or death. In women having pelvic radiotherapy for gynaecological cancer it gave no consistent benefit, and diarrhoea was more common than in controls at week 4. Bacterial probiotics such as lactobacilli and bifidobacteria, and synbiotics, are covered separately, as effects differ by strain.
Safety and when to see a clinician
- Bloodstream yeast infection: a 2023 review of 108 cases of Saccharomyces fungaemia found 73 had been given the S. boulardii probiotic, with long intensive-care stays, tube or intravenous feeding and diarrhoea as the leading risk factors; overall mortality among the 108 was 36.1%. In 5 Finnish university hospitals over 10 years, at least 20 of 46 patients with this infection were taking the probiotic (odds ratio 14 against other bloodstream infections), and in US hospitals 0.11% of recipients developed it, more often in intensive care. Anyone in intensive care, with a central venous catheter, on tube or drip feeding, or with a weakened immune system needs the care team's agreement before any dose.
- Spread to other patients: opening packets spread the yeast through the air, onto surfaces and onto hands, and all the patients in one report of fungaemia had an indwelling vascular catheter; in an intensive care unit, three roommates of treated patients developed fungaemia, probably through central-line contamination. In hospital, let the care team handle any probiotic.
- Everyday side effects: in the 2025 Cochrane review the commonest events, in both probiotic and control groups, were cramping, nausea, fever, soft stools, wind and taste changes, and short courses were judged unlikely to cause harm in people on antibiotics whose immune systems work normally. A 2009 review noted more thirst and constipation on S. boulardii.
- When diarrhoea needs a doctor: C. difficile needs prescription treatment, and S. boulardii was tested only as an add-on to it. Get medical advice for diarrhoea during or after antibiotics with fever, belly pain or blood in the stool, and do not stop an antibiotic yourself because of loose stools; ask the prescriber.
- Children, older people and pregnancy: any amount for a child is for the child's own doctor to set, and in preterm infants it is a decision for the neonatal team. A hospital series of 10 fungaemia cases included three people aged 80 or more with no other risk factor, and its authors suggested older age should rule these probiotics out. In pregnancy or while breastfeeding, check with your midwife or obstetric team.
What saccharomyces boulardii is good for
How we grade →Strong evidence
Antibiotic-Associated Diarrhea Risk: Improves
All 1 outcome ↓
Evidence by condition
- Strong
- Moderate
- Limited
- Very limited
AAntibiotic-Associated Diarrhea (AAD)
▲ Antibiotic-Associated Diarrhea Risk1 outcome · 5 studies
Antibiotic-Associated Diarrhea (AAD): all the evidence on its own page
| Grade | Outcome | Effect | Size and studies |
|---|---|---|---|
| A | Antibiotic-Associated Diarrhea RiskModerate ImprovementStudied as: Oral Saccharomyces boulardii (freeze-dried yeast; the strain with trial evidence is CNCM I-745, per review 38286962), about 500 mg-1 g a day in 2 doses (1 g/day in 7872284), started within 48-72 hours of the antibiotic and continued until 3-7 days after it ends; harms: rare Saccharomyces fungaemia, mainly in people with a central venous catheter, in intensive care or with a damaged gut lining (Finland: S. boulardii use OR 14 among fungaemia cases, 34287140; US inpatients: 0.11% of recipients, ICU OR 6.6, 34585799), so not for people who are critically ill, have a central line or are immunocompromisedStudies that measured antibiotic-associated diarrhea risk (5 studies)
| Improves | Moderate effect · 5 studiesReviewed |
Studies cited
41 studies from PubMed
- Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea.
- Saccharomyces boulardii to Prevent Antibiotic-Associated Diarrhea: A Randomized, Double-Masked, Placebo-Controlled Trial.
- Systematic review with meta-analysis: Saccharomyces boulardii supplementation and eradication of Helicobacter pylori infection.
- Saccharomyces boulardii as an Adjunct to Helicobacter pylori Eradication Therapy: A Systematic Review and Meta-Analysis.
- Systematic review with meta-analysis: Saccharomyces boulardii for treating acute gastroenteritis in children-a 2020 update.
- Saccharomyces boulardii does not prevent relapse of Crohn's disease.
- Epidemiology of Saccharomyces fungemia: A systematic review.
- Fungemia and Other Fungal Infections Associated with Use of Saccharomyces boulardii Probiotic Supplements.
- Systematic review and meta-analysis of Saccharomyces boulardii in adult patients.
- Prevention of beta-lactam-associated diarrhea by Saccharomyces boulardii compared with placebo.
Show all 41 studies
- Prophylactic Saccharomyces boulardii in the prevention of antibiotic-associated diarrhea: a prospective study.
- Saccharomyces boulardii for the Prevention of Antibiotic-Associated Diarrhea in Hospitalized Patients Receiving Antibiotics: A Single-Center, Randomized, Double-Blind, Placebo-Controlled Trial.
- Saccharomyces boulardii for the prevention of antibiotic-associated diarrhea in adult hospitalized patients: a single-center, randomized, double-blind, placebo-controlled trial.
- Probiotics for the prevention of pediatric antibiotic-associated diarrhea.
- [A prospective randomized controlled study on probiotics for the prevention of antibiotic-associated diarrhea in infants and young children].
- A randomized placebo-controlled trial of Saccharomyces boulardii in combination with standard antibiotics for Clostridium difficile disease.
- The search for a better treatment for recurrent Clostridium difficile disease: use of high-dose vancomycin combined with Saccharomyces boulardii.
- Efficacy and safety of Saccharomyces boulardii as adjunct therapy with Vancomycin in treating Clostridioides difficile infection: A randomized controlled trial.
- Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children.
- AGA Clinical Practice Update on Management of Clostridioides difficile Infection in Adults: Expert Review.
- The effect of Saccharomyces boulardii supplementation on Helicobacter pylori eradication in children: a systematic review and meta-analysis of Randomized controlled trials.
- The effect of supplementing with Saccharomyces boulardii on bismuth quadruple therapy for eradicating Helicobacter pylori: a systematic review and meta-analysis of randomized controlled trials.
- Probiotic monotherapy and Helicobacter pylori eradication: A systematic review with pooled-data analysis.
- Which Probiotic Is the Most Effective for Treating Acute Diarrhea in Children? A Bayesian Network Meta-Analysis of Randomized Controlled Trials.
- Impact of Probiotics on Children with Acute Gastroenteritis: Results from an Umbrella Meta-Analysis.
- Probiotics for treating acute infectious diarrhoea.
- Are probiotics and prebiotics effective in the prevention of travellers' diarrhea: A systematic review and meta-analysis.
- Meta-analysis of probiotics for the prevention of traveler's diarrhea.
- Investigating the influence of probiotics in preventing Traveler's diarrhea: Meta-analysis based systematic review.
- A randomized, double-blind, placebo-controlled multicenter trial of saccharomyces boulardii in irritable bowel syndrome: effect on quality of life.
- Strain-specific and outcome-specific efficacy of probiotics for the treatment of irritable bowel syndrome: A systematic review and meta-analysis.
- Strain-Specific Systematic Review with Meta-Analysis of Probiotics Efficacy in the Treatment of Irritable Bowel Syndrome.
- Saccharomyces boulardii prevents diarrhea in critically ill tube-fed patients. A multicenter, randomized, double-blind placebo-controlled trial.
- Saccharomyces boulardii in patients with severe acute pancreatitis: a single center, open-label randomized controlled trial.
- Effect and Safety of Saccharomyces boulardii for Neonatal Necrotizing Enterocolitis in Pre-term Infants: A Systematic Review and Meta-Analysis.
- Impact of Saccharomyces boulardii on acute gastrointestinal toxicities in patients undergoing pelvic radiotherapy for gynecologic cancers: a randomized controlled trial.
- Incidence of Saccharomyces cerevisiae fungemia in hospitalised patients administered Saccharomyces boulardii probiotic.
- Possible role of catheters in Saccharomyces boulardii fungemia.
- Outbreak of Saccharomyces cerevisiae subtype boulardii fungemia in patients neighboring those treated with a probiotic preparation of the organism.
- Prevention of Clostridium difficile infection with Saccharomyces boulardii: a systematic review.
- Saccharomyces cerevisiae fungemia: Risk factors, outcome and links with S. boulardii-containing probiotic administration.