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What S. boulardii is
Saccharomyces boulardii is a strain of yeast, closely related to baker's yeast. Most probiotics are bacteria (Lactobacillus, Bifidobacterium). Because S. boulardii is a fungus, antibacterial antibiotics don't harm it, so it can be taken at the same time as an antibiotic course. Antifungal medicines, though, will kill it.
It passes through the gut without settling there permanently; levels fall within days of stopping. While it's present, it's thought to work by blocking toxins made by harmful bacteria (such as C. difficile), supporting the gut lining, and dampening inflammation.
Probiotic effects are strain-specific. Much of the research uses the strain CNCM I-745, the strain in several branded pharmacy products. Evidence for one probiotic doesn't carry over to a different species or strain.
Clinical evidence — what the trials show
| Study | What was tested | Design | Key finding | Grade |
|---|---|---|---|---|
| Szajewska & Kołodziej (2015) — Aliment Pharmacol Ther doi:10.1111/apt.13344 | S. boulardii with antibiotics vs placebo or nothing | Meta-analysis, 21 RCTs, n = 4,780 | Antibiotic-associated diarrhoea fell from 17.4% to 8.2% in adults and from 20.9% to 8.8% in children. | A |
| Feizizadeh et al. (2014) — Pediatrics PubMed 24958586 | S. boulardii for acute diarrhoea in children | Meta-analysis, 22 trials | Diarrhoea lasted 19.7 hours less, with fewer stools on days 2 and 3. No serious adverse effects reported in these trials. | A |
| Su et al. (2020) — AGA guideline, Gastroenterology gastrojournal.org | Probiotics to prevent C. difficile during antibiotics | Guideline, evidence review | S. boulardii cut C. difficile risk (RR 0.41). The AGA gives a conditional recommendation, based on low-quality evidence. | B |
| EMA safety review (2017) and Rannikko et al. (2021) — Emerg Infect Dis wwwnc.cdc.gov | Fungaemia linked to S. boulardii products | Safety review; case series | Rare bloodstream yeast infections, mostly in critically ill or immunocompromised patients and those with central venous catheters. Some were fatal. | B |
Guidelines disagree on C. difficile. The American Gastroenterological Association (2020) conditionally suggests certain probiotics, including S. boulardii, during antibiotics. [3] The American College of Gastroenterology (2021) recommends against probiotics for C. difficile prevention. [6] For ordinary antibiotic-associated diarrhoea, the trial evidence is more consistent. [1]
How much to take
Evidence-based protocol
With antibiotics: 250–500 mg a day (often 250 mg twice daily), started on the same day as the antibiotic and continued for its full course. Trials in the meta-analysis mostly used doses in this range. [1] Acute diarrhoea in children: 250–750 mg a day for 5–7 days, alongside ORS and zinc, on a doctor's advice. [2] Timing: you can take it at the same time as antibacterial antibiotics. Don't take it with antifungal medicines, which kill it. Storage: check the pack; lyophilised (freeze-dried) sachets and capsules are usually stable at room temperature.
India-specific context
Cheap, everywhere, and widely prescribed
Antibiotic use in India is high, and a lot of it comes without a prescription. That makes antibiotic-associated diarrhoea common, and S. boulardii is a cheap, sensible add-on. For children with acute diarrhoea, the priority is always rehydration with ORS plus zinc; S. boulardii can shorten the illness by about a day. [2] Seek care urgently for blood in the stool, high fever, or signs of dehydration.
What's on sale in India
| Product | Price | Contents | Evidence match | Our take |
|---|---|---|---|---|
| Econorm (Dr. Reddy's) sachet / capsule | ~₹60–80 per 250 mg sachet | S. boulardii 250 mg | Matches trial doses | The most widely available S. boulardii product in India. Sold at chemists. |
| Other S. boulardii pharmacy brands | Varies | S. boulardii, usually 250 mg | Check the strain | Several brands exist. Prefer those naming the strain (e.g. CNCM I-745). |
| Multi-strain bacterial probiotics | ₹499–799 / 30–60 caps | Lactobacillus / Bifidobacterium blends | Different organisms | Different evidence entirely. High CFU counts don't make them a substitute for S. boulardii during antibiotics. |
Prices are approximate, from Indian pharmacy listings (2026). Bacterial probiotic price range is from our product database. We haven't yet lab-tested an S. boulardii product.
Safety
Fungaemia in very sick patients
Rare bloodstream yeast infections have occurred, mostly in critically ill or immunocompromised patients and those with central venous catheters. The EMA says the risk outweighs the benefit in these patients. [4][5]
Spread to nearby patients
Opening capsules or sachets near a patient with a central line can contaminate it. Hospitals should handle the product away from such patients. [4]
Antifungal medicines
Oral antifungals (such as fluconazole) kill S. boulardii, so taking them together wastes the probiotic.
Mild bloating
Mild gas or bloating is the most common side effect in healthy users and usually settles.
Commonly taken together
ORS and zinc
Core treatmentFor childhood diarrhoea, ORS and zinc come first; S. boulardii is an add-on. See our zinc deep-dive.
Antibiotics
Take togetherStart it with the antibiotic course to cut diarrhoea risk. [1]
Psyllium husk
Gut supportSoluble fibre supports stool form after diarrhoea settles. See our psyllium deep-dive.
Bacterial probiotics
Different evidenceSome bacterial strains have their own evidence; they aren't interchangeable with S. boulardii.
Scoring rubric — full breakdown
1. Evidence quality
Several meta-analyses of randomised trials support antibiotic-associated and acute childhood diarrhoea. We deduct for heterogeneous, often small trials and conflicting C. difficile guidelines. [1][2][6]
2. Dosage confidence
Trials cluster around 250–750 mg a day, and the common Indian 250 mg format fits. [1]
3. India market fit
High antibiotic use and childhood diarrhoea make it relevant, and it's cheap and sold at every chemist.
4. Safety profile
Very safe in healthy people, but rare, sometimes fatal fungaemia in critically ill patients means clear exclusions. [4][5]
5. Label accuracy (tested)
Pharmacy products are regulated as medicines, but many don't state the strain, and we haven't lab-tested one.
References
- 1Szajewska H, Kołodziej M. Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea. Aliment Pharmacol Ther. 2015;42(7):793–801.doi:10.1111/apt.13344
- 2Feizizadeh S, Salehi-Abargouei A, Akbari V. Efficacy and safety of Saccharomyces boulardii for acute diarrhea. Pediatrics. 2014;134(1):e176–91.PubMed 24958586
- 3Su GL, et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020.gastrojournal.org
- 4European Medicines Agency (CMDh). Saccharomyces boulardii: scientific conclusions and grounds for variation (PSUSA/00009284/201702), risk of fungaemia.ema.europa.eu
- 5Rannikko J, et al. Fungemia and other fungal infections associated with use of Saccharomyces boulardii probiotic supplements. Emerg Infect Dis. 2021;27(8).wwwnc.cdc.gov
- 6International Scientific Association for Probiotics and Prebiotics. The American College of Gastroenterology recommends against use of probiotics for primary or secondary prevention of C. difficile. 2021.isappscience.org
Medical note. This page is educational and not a diagnosis. See a doctor urgently for diarrhoea with blood, high fever, severe pain or signs of dehydration, especially in children and older adults.
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