Saccharomyces boulardii
Saccharomyces boulardii is a probiotic yeast. What reviews and guidelines found for antibiotic-associated and C. difficile diarrhea, children's diarrhea and IBS, plus the rare bloodstream infections.
Content last updated . This page has not been medically reviewed.
What is Saccharomyces boulardii good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Preventing antibiotic-associated diarrhoea
Clinically supportedS. boulardii CNCM I-745 has been studied to lower the chance of diarrhoea during antibiotic treatment, especially in children.
Supplements: ESPGHAN strongly recommended it for children with risk factors; adult evidence is lower certainty. Applies to this strain and this use.
Preventing C. difficile diarrhoea in people on antibiotics
Preliminary or mixedThe AGA found a lower rate of C. difficile diarrhoea with S. boulardii, with low certainty, and conditionally suggests it.
Supplements: Low-certainty evidence; people valuing cost or harm avoidance may reasonably choose none.
Add-on to C. difficile treatment
Preliminary or mixedIn the largest trial (124 adults) diarrhoea stopped more often and recurred less when added to standard antibiotics. Guidelines recommend this only within clinical trials.
Supplements: Low certainty; not a substitute for treatment.
Children's acute infectious diarrhoea
Preliminary or mixedSome trials found shorter diarrhoea, but a Cochrane review found little or no difference in the lowest-bias trials.
Supplements: Mixed; the AGA suggests against probiotics for children's gastroenteritis in North America.
Irritable bowel syndrome
Preliminary or mixedStudies found no difference in abdominal pain versus placebo, and a 2026 review called results conflicting.
Supplements: No reliable benefit shown.
Add-on to H. pylori treatment
Preliminary or mixedWGO tables report higher eradication and fewer treatment side effects when added to standard treatment; no evidence it works alone.
Supplements: Limited; read via the site page summary.
Crohn's disease
Not enough evidenceNo clear benefit was seen when two S. boulardii studies were pooled.
Supplements: No evidence of benefit.
Product quality and strain labelling
Not enough evidenceResults belong to a named strain (usually CNCM I-745); a label may not match the contents because probiotics are regulated as food in the UK.
Supplements: Check the strain code against the study.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (2)
- Digestive SupportClinically supported
Studied mainly to prevent diarrhoea linked to antibiotics (S. boulardii CNCM I-745). Results are for this yeast and these uses only, with low certainty in the AGA review; trials for other uses are mixed.
- Gut HealthPreliminary or mixed
Trials look at specific gut problems (antibiotic-linked diarrhoea, some children's diarrhoea), not general gut health. Evidence is mixed and strain-specific.
Body systems (2)
- Digestive SystemClinically supported
Studied mainly to prevent diarrhoea linked to antibiotics (S. boulardii CNCM I-745). Results are for this yeast and these uses only, with low certainty in the AGA review; trials for other uses are mixed.
- Gut HealthClinically supported
Studied mainly to prevent diarrhoea linked to antibiotics (S. boulardii CNCM I-745). Results are for this yeast and these uses only, with low certainty in the AGA review; trials for other uses are mixed.
Body parts (1)
- GutDocumented risk
Rare yeast bloodstream infections (fungaemia) have been reported after S. boulardii use, mainly in intensive-care patients, people with central venous lines or weak immunity. Ask a clinician first in those situations.
Functional actions (1)
- Digestive SupportClinically supported
Studied mainly to prevent diarrhoea linked to antibiotics (S. boulardii CNCM I-745). Results are for this yeast and these uses only, with low certainty in the AGA review; trials for other uses are mixed.
Root causes (2)
- Medication Side EffectsClinically supported
Diarrhoea caused by antibiotics is the best-studied use: ESPGHAN gave a strong recommendation in children with risk factors, and the AGA conditionally suggests it for C. difficile prevention, with low-quality evidence.
- Gut DysbiosisPreliminary or mixed
Antibiotics upset the gut community and the yeast is studied alongside them (antibiotics do not typically kill yeast). Whether it corrects 'dysbiosis' itself was not shown in the sources read.
Conditions & symptoms (3)
- Antibiotic-Associated DiarrheaClinically supported
ESPGHAN (2016) strongly recommended S. boulardii or L. rhamnosus GG for children on antibiotics who have risk factors (moderate-quality evidence). Evidence in adults is lower certainty.
- FungemiaDocumented risk
Yeast bloodstream infection has been reported after S. boulardii-containing probiotics, mainly in intensive-care patients and people with central lines; a Belgian series of 10 patients with S. cerevisiae fungaemia had 70% with a central line and half died. Reported as rare but life-threatening.
- Clostridium Difficile InfectionPreliminary or mixed
AGA review: lower risk of C. difficile diarrhoea in people on antibiotics (risk ratio 0.41, low certainty); as an add-on to treatment, low-certainty benefit. The AGA guideline recommends probiotics for treatment only within a clinical trial. Never a replacement for treatment.
Documented risks and interactions (2)
- Yeast bloodstream infection (fungaemia) risk. Rare but serious bloodstream infections with this yeast have been reported, mostly in intensive-care patients and people with central lines or weak immunity.
- Mild digestive side effects. In trials the usual side effects were mild stomach symptoms, with one trial showing more constipation than placebo.
What it is
Saccharomyces boulardii is a yeast used as a probiotic. NCCIH lists it among the non-bacterial organisms used in probiotic products. [5] It is not a Lactobacillus or Bifidobacterium; see Lactobacillus and Bifidobacterium probiotics. Research papers name the strain, most often CNCM I-745. [6] Case reports sometimes describe the infecting organism as Saccharomyces cerevisiae after S. boulardii use. [2] For a deeper look at antibiotic diarrhea and C. difficile, see the S. boulardii antibiotic and C. diff page.Evidence labels: promising but limited (some trials, low certainty), mixed (trials disagree), insufficient evidence. "CoE" is certainty of evidence as graded by reviewers. Trial amounts are study amounts, not advice.
Why a yeast is interesting during antibiotics
The AGA technical review (US, 2020) notes that antibiotics do not typically kill yeast. How S. boulardii works is still unclear. [7]What the research found, by use
| Use | What the source found | Label |
|---|---|---|
| Preventing C. difficile-associated diarrhea in people on antibiotics | The AGA found S. boulardii was the only single-strain probiotic with a significant effect (risk ratio 0.41, low CoE). [7] | Promising but limited |
| Treating C. difficile infection alongside standard antibiotics | In the largest study (124 adults), diarrhea stopped more often (RR 1.33) and recurred less (RR 0.59), both low CoE. [7] The AGA guideline recommends probiotics here only in the context of a clinical trial. [8] | Promising but limited |
| Children's acute infectious diarrhea | In 10 of 22 trials, diarrhea was about 29 hours shorter, with very low certainty. [7] A Cochrane review of 82 trials found little or no difference in diarrhea lasting 48 hours or more in the lowest-bias trials, with similar results in analyses limited to this yeast. [9] | Mixed |
| Preventing antibiotic-associated diarrhea in children | ESPGHAN (European pediatric gastroenterology society, 2016) gave a strong recommendation, with moderate-quality evidence, for S. boulardii or Lactobacillus rhamnosus GG if probiotics are considered for children with risk factors. [10] | Promising but limited |
| IBS | Three studies (232 adults) found no difference in abdominal pain versus placebo (very low CoE). [7] A 2026 review called the results for CNCM I-745 conflicting. [11] | Mixed |
| Pediatric acute diarrhea, trials done in China | A 2025 meta-analysis of 10 Chinese trials (1,125 children) found shorter illness. One author declared consulting work for companies (see the paper's conflict-of-interest statement). [12] | Promising but limited |
The 228-trial review also found that CNCM I-745 worked differently across diseases, so one result should not be carried to another condition. [6] For children's gastroenteritis in North America the AGA suggests against probiotics, noting that the trials behind the three strain-specific reviews were done outside North America. [8][7]
Studied amounts
The largest C. difficile treatment study used 1 g, or 3 x 10^10 CFU, a day. That is what the trial used and not a recommendation. [7] The sources we read did not give a best amount for the yeast. A clinician or pharmacist decides what is right for a person.Checking a product
Look for the strain code on the label and compare it with the study you are relying on. [6] The NHS notes that, because probiotics are regulated as food, we cannot always be sure a product contains the organism or the amount stated. [13] See probiotic strains and labels and quality testing and certifications.If you have diarrhea
Most diarrhea is caused by a stomach bug and passes within days; the NHS says the most important thing is plenty of fluids. [14] The NHS advises urgent advice for bloody diarrhea, diarrhea over 7 days, signs of dehydration in a child under 5, or any worry about a baby under 12 months. [14] In the US, call 911 for an emergency. A probiotic is not a substitute for medical care or for a prescribed treatment.Frequently asked questions
Is Saccharomyces boulardii safe?
For most healthy people probiotics appear safe. [13] Rare yeast bloodstream infections have been reported, mainly in critically ill people with central lines. [1]
Can I take it with antibiotics?
The AGA notes that antibiotics do not typically kill yeast, which is part of why it is studied alongside them. [7] Ask your prescriber or pharmacist about your situation, and never stop a prescribed antibiotic on your own.
Does S. boulardii help IBS?
Evidence is mixed. The AGA saw no pain difference in three small studies, and a 2026 review found conflicting results. [7][11]
Does it prevent C. difficile?
The AGA found a possible benefit for prevention in people on antibiotics, with low certainty. [7] Its guideline lists this yeast among options it suggests, but only as a conditional recommendation. [8]
What does CNCM I-745 mean?
It is a strain code used in research papers to name the exact yeast that was tested. [6] Compare it with the code on a product label before assuming a study applies.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety first: who should not self-start this yeast
Other safety points
- Healthy adults. The NHS says that with a healthy immune system probiotics shouldn't cause unpleasant side effects. [13]
- Side effects in trials. In the C. difficile trials the AGA reported mild stomach symptoms, with one study showing more constipation on this yeast. [7]
- Medicines. Interactions were not described in the sources we read, and we found no kidney- or liver-specific guidance (Proper evidence not found). Ask a pharmacist; see how medicine interactions work.
- Pregnancy and breastfeeding, and before surgery. We did not read a source on this yeast for these situations. Ask a clinician.
References
- Vinayagamoorthy K et al. Med Mycol 2023. Epidemiology of Saccharomyces fungemia: A systematic review. PMID 36806741. Read 2026-10-22.
- Dholakia V et al. IDCases 2025. Probiotic paradox: Saccharomyces cerevisiae fungemia after S. boulardii use in severe pancreatitis. PMID 41476631. Read 2026-10-22.
- Lee YM. Microorganisms 2025. Central Line-Related Bloodstream Infection by Saccharomyces cerevisiae Following Probiotic Use in a Patient with Clostridioides difficile Colitis: A Case Report. PMID 41597590. Read 2026-10-22.
- Poncelet A et al. Infect Dis Now 2021. Saccharomyces cerevisiae fungemia: Risk factors, outcome and links with S. boulardii-containing probiotic administration. PMID 33934809. Read 2026-10-22.
- NCCIH (US National Center for Complementary and Integrative Health). Probiotics: Usefulness and Safety. Read 2026-10-22.
- McFarland LV, Evans CT, Goldstein EJC. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. Front Med 2018. PMID 29868585. Read 2026-10-22.
- Preidis GA et al. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology 2020 (full text read via PMC8018518). PMID 32531292. Read 2026-10-22.
- Su GL et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology 2020 (guideline text read from a hosted copy of the published PDF). PMID 32531291. Read 2026-10-23.
- Collinson S et al. Cochrane Database Syst Rev 2020 (CD003048). Probiotics for treating acute infectious diarrhoea. PMID 33295643. Read 2026-10-22.
- Szajewska H et al. (ESPGHAN Working Group) J Pediatr Gastroenterol Nutr 2016. Probiotics for the Prevention of Antibiotic-Associated Diarrhea in Children. PMID 26756877. Read 2026-10-22.
- Strain-Specific Systematic Review with Meta-Analysis of Probiotics Efficacy in the Treatment of Irritable Bowel Syndrome. PMID 41682832. Read 2026-10-22.
- McFarland LV, Li T. Front Cell Infect Microbiol 2025. Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis. PMID 40535538. Read 2026-10-22.
- NHS (UK). Probiotics. Page last reviewed 24 November 2022. Read 2026-10-22.
- NHS (UK). Diarrhoea and vomiting. Read 2026-10-22.