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S. Boulardii for Antibiotic-Associated Diarrhea: What the Trials Show, and When Probiotics Don't Help

S. boulardii, a probiotic yeast, roughly halved antibiotic-associated diarrhea in pooled trials (17.4% to 8.2% in adults; grade B), but a 15-hospital German trial in adults was stopped early for showing no benefit, and it did not clearly lower C. difficile infection in adults (grade B). It eased diarrhea from H. pylori antibiotic treatment (grade A). It can cause rare bloodstream yeast infections, so skip it if you are critically ill or have an IV line.

Published How we grade evidenceEditorial policy

The short version

  • S. boulardii to prevent antibiotic diarrhea in adults: about half as many cases in pooled trials, but a 15-hospital trial found none fewer. Grade B (Szajewska 2015; Ehrhardt 2016).
  • S. boulardii and C. difficile in adults: no clear drop. Grade B (Szajewska 2015).
  • Probiotics in general and C. difficile: cases fell from 3.2% to 1.6% in pooled trials, on low-certainty evidence; a 2026 expert guideline advises against them for this. Grade B (Esmaeilinezhad 2025; Fischer 2026).
  • Older adults in hospital: two large trials of bacterial probiotics found no benefit. Grade B (Allen 2013; Rajkumar 2020).
  • During H. pylori treatment: S. boulardii roughly halved diarrhea from the antibiotics. Grade A (Szajewska 2015).
  • Yogurt: no consistent effect. Grade C (Patro-Golab 2015).

Antibiotics kill helpful gut bacteria along with the harmful ones, and loose stools are a common side effect. The serious form is C. difficile infection, a gut infection that is up to 10 times more likely while you take an antibiotic and is most common in people 65 and older and in hospitals or nursing homes (CDC). Probiotics are live microbes taken to restore the balance. Results depend on the strain, so this guide keeps them apart.

Does S. boulardii prevent antibiotic-associated diarrhea?

Grade B. S. boulardii (Saccharomyces boulardii) is a yeast, not a bacterium. A 2015 meta-analysis pooled 21 randomized trials with 4,780 people. In the 15 adult trials (3,114 people), antibiotic-associated diarrhea fell from 17.4% to 8.2% (risk ratio 0.49) (Szajewska 2015). An earlier review of adult trials found a similar drop (risk ratio 0.47) (McFarland 2010).

The best-run adult trial did not agree. At 15 German hospitals, adults on antibiotics took 250 mg capsules of S. boulardii twice a day or a placebo, starting within 24 hours of the first antibiotic dose and for a week after the last. The trial was stopped early for futility after 477 people: 21 cases of diarrhea on the yeast and 19 on placebo (Ehrhardt 2016). Its patients had no special risk factors, so the benefit may be smaller where diarrhea is less common.

Does it prevent C. difficile infection?

Grade B for S. boulardii in adults: no clear drop. In 9 adult trials (1,441 people), the risk ratio was 0.8, a range that includes no effect; the reduction was clear only in 2 trials in children (Szajewska 2015).

Grade B for probiotics as a group, with a small, uncertain benefit. The 2025 Cochrane review pooled 38 trials (13,179 people of all ages on antibiotics): C. difficile diarrhea occurred in 1.6% on probiotics and 3.2% on control, so about 65 people need to take them to spare one case. The reviewers rated the evidence low, and 28 of the 47 studies had ties to probiotic companies (Esmaeilinezhad 2025). A 2026 expert review from the American Gastroenterological Association advises against probiotics to prevent a first or repeat C. difficile infection (Fischer 2026).

Timing may matter: an analysis of 36 adult trials concluded that probiotics should start as early as possible in the antibiotic course (Liao 2021).

Do bacterial probiotics, such as lactobacilli, work as well?

Grade B. Pooled, they help a little. Across 40 trials (13,419 people), antibiotic diarrhea fell from 27.4% to 23% (risk ratio 0.67), on low-certainty evidence (Esmaeilinezhad 2025); an analysis of 36 adult trials (9,312 people) found a 38% lower risk (Liao 2021).

Grade B for no benefit in older hospital patients, where the biggest trials were done. In 2,981 inpatients aged 65 and over, a daily lactobacilli and bifidobacteria preparation for 21 days left diarrhea unchanged (10.8% against 10.4%) (Allen 2013). In 1,127 patients over 55, a probiotic yogurt drink made no difference (19.3% against 17.9%) (Rajkumar 2020).

Grade C for Lactobacillus rhamnosus GG (LGG) in adults. Its benefit was clear in children, but in 6 adult trials (863 people) the drop was not significant, except during H. pylori treatment (Szajewska 2015).

Does S. boulardii help during H. pylori treatment?

Grade A. H. pylori is a stomach bacterium treated with a combination of antibiotics and an acid blocker, which often upsets the gut. In 11 trials (2,200 people), adding S. boulardii cut diarrhea from the treatment by about half (risk ratio 0.51, high-quality evidence) and nausea too. Slightly more people cleared the infection, 80% against 71% (Szajewska 2015).

Does yogurt or kefir do the same job?

Grade C. Not reliably. A 2015 review found only 2 small yogurt trials and no consistent effect (Patro-Golab 2015). In a family practice, 369 people on a week of antibiotics ate live yogurt, ordinary yogurt or none; diarrhea rates of 7%, 11% and 14% were not a clear difference (Conway 2007). In 314 hospital patients, a probiotic yogurt did no better than a plain one (23.0% against 17.6%) (Velasco 2019). Food is fine to eat; just don't count on it.

What about children?

A 2019 Cochrane review of 33 trials in children found antibiotic diarrhea in 8% on probiotics against 19% on control (Guo 2019). For a child, ask the clinician who prescribed the antibiotic; this guide gives no children's amounts.

What we'd skip

  • Probiotics in place of C. difficile treatment. It needs prescription antibiotics, and the 2026 expert review advises against probiotics even to stop it coming back (Fischer 2026).
  • S. boulardii if you are critically ill, fed through a tube or a vein, or have a central IV line. Bloodstream yeast infections cluster in exactly these patients (Vinayagamoorthy 2023).
  • Probiotic yogurt drinks to protect older hospital patients. Two large trials found no benefit (Rajkumar 2020; Velasco 2019).
  • Glutamine, zinc or prebiotic fiber for antibiotic diarrhea. Our protocol page lists them; we found no adult trial of any of them for this.

Safety and interactions

  • Bloodstream yeast infection (fungemia). It is rare, but it is the main risk. A review of 108 cases of Saccharomyces fungemia found that about two-thirds (73) had been given the S. boulardii probiotic; intensive care, tube or IV feeding, and diarrhea were the main risk factors, and 36.1% of all the patients died (Vinayagamoorthy 2023). In 5 Finnish hospitals over 10 years, at least 20 of 46 patients with this infection were taking the probiotic (Rannikko 2021).
  • It can spread to others. Opening capsules or sachets spreads the yeast on hands and surfaces: in one report all 4 patients had an IV catheter (Hennequin 2000), and in an intensive care unit 3 roommates of treated patients were infected (Cassone 2003). In hospital, leave probiotics to the care team.
  • Everyday side effects were mild (cramps, nausea, soft stools, gas, taste changes) and no more common than on control (risk ratio 0.86). The Cochrane reviewers judged short courses unlikely to cause harm in people whose immune systems work normally (Esmaeilinezhad 2025).
  • Interactions: no interaction studies were found. If you have a weak immune system (for example from chemotherapy, a transplant or high-dose steroids), ask your care team before any probiotic.

When to see a doctor

  • Diarrhea while you're on an antibiotic or after one, especially with fever, belly pain or tenderness, or loss of appetite: contact a clinician, who may test for C. difficile (CDC).
  • Right away for blood in the stool, severe belly pain or swelling, signs of dehydration (very little urine, dizziness), or diarrhea that won't stop.
  • If you are 65 or older, were recently in hospital, have a weak immune system, or have had C. difficile before: your risk is higher, so call early (CDC).

Don't stop an antibiotic on your own because of loose stools; ask the prescriber or pharmacist. If you are pregnant or breastfeeding, ask your doctor or midwife before taking a probiotic.

FAQ

Which probiotic is best with antibiotics? S. boulardii has the most adult trials for antibiotic diarrhea (grade B), but the largest hospital trial found no benefit, and bacterial blends did no better in older inpatients.

Should I take S. boulardii to avoid C. difficile? In adults, it did not clearly lower C. difficile (grade B), and a 2026 expert review advises against probiotics for this.

When should probiotics be started? In the trials they started with the antibiotic, usually within 1 to 2 days, and ran a few days to a week past the last dose.

Is S. boulardii safe? For healthy people on a short course, side effects were mild. It can cause rare but serious bloodstream yeast infections in people who are very ill or have an IV line.

Sources

  1. Szajewska H, et al. Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea. Aliment Pharmacol Ther. 2015. PubMed 26216624 · doi:10.1111/apt.13344
  2. Ehrhardt S, et al. Saccharomyces boulardii to Prevent Antibiotic-Associated Diarrhea: A Randomized, Double-Masked, Placebo-Controlled Trial. Open Forum Infect Dis. 2016. PubMed 26973849 · doi:10.1093/ofid/ofw011
  3. Esmaeilinezhad Z, et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev. 2025. PubMed 40931979 · doi:10.1002/14651858.CD006095.pub5
  4. Fischer M, et al. AGA Clinical Practice Update on Management of Clostridioides difficile Infection in Adults: Expert Review. Clin Gastroenterol Hepatol. 2026. PubMed 42383946 · doi:10.1016/j.cgh.2026.05.007
  5. Allen SJ, et al. Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial. Lancet. 2013. PubMed 23932219 · doi:10.1016/S0140-6736(13)61218-0
  6. Rajkumar C, et al. Do probiotics prevent antibiotic-associated diarrhoea? Results of a multicentre randomized placebo-controlled trial. J Hosp Infect. 2020. PubMed 32035998 · doi:10.1016/j.jhin.2020.01.018
  7. Szajewska H, et al. Systematic review with meta-analysis: Saccharomyces boulardii supplementation and eradication of Helicobacter pylori infection. Aliment Pharmacol Ther. 2015. PubMed 25898944 · doi:10.1111/apt.13214
  8. Patro-Golab B, et al. Yogurt for treating antibiotic-associated diarrhea: Systematic review and meta-analysis. Nutrition. 2015. PubMed 25933485 · doi:10.1016/j.nut.2014.11.013
  9. McFarland LV. Systematic review and meta-analysis of Saccharomyces boulardii in adult patients. World J Gastroenterol. 2010. PubMed 20458757 · doi:10.3748/wjg.v16.i18.2202
  10. Liao W, et al. Probiotics for the Prevention of Antibiotic-associated Diarrhea in Adults: A Meta-Analysis of Randomized Placebo-Controlled Trials. J Clin Gastroenterol. 2021. PubMed 33234881 · doi:10.1097/MCG.0000000000001464
  11. Szajewska H, et al. Systematic review with meta-analysis: Lactobacillus rhamnosus GG in the prevention of antibiotic-associated diarrhoea in children and adults. Aliment Pharmacol Ther. 2015. PubMed 26365389 · doi:10.1111/apt.13404
  12. Conway S, et al. Does eating yogurt prevent antibiotic-associated diarrhoea? A placebo-controlled randomised controlled trial in general practice. Br J Gen Pract. 2007. PubMed 18252070 · doi:10.3399/096016407782604811
  13. Velasco M, et al. Probiotic Yogurt for the Prevention of Antibiotic-associated Diarrhea in Adults: A Randomized Double-blind Placebo-controlled Trial. J Clin Gastroenterol. 2019. PubMed 30439760 · doi:10.1097/MCG.0000000000001131
  14. Guo Q, et al. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev. 2019. PubMed 31039287 · doi:10.1002/14651858.CD004827.pub5
  15. Vinayagamoorthy K, et al. Epidemiology of Saccharomyces fungemia: A systematic review. Med Mycol. 2023. PubMed 36806741 · doi:10.1093/mmy/myad014
  16. Rannikko J, et al. Fungemia and Other Fungal Infections Associated with Use of Saccharomyces boulardii Probiotic Supplements. Emerg Infect Dis. 2021. PubMed 34287140 · doi:10.3201/eid2708.210018
  17. Hennequin C, et al. Possible role of catheters in Saccharomyces boulardii fungemia. Eur J Clin Microbiol Infect Dis. 2000. PubMed 10706174 · doi:10.1007/s100960050003
  18. Cassone M, et al. Outbreak of Saccharomyces cerevisiae subtype boulardii fungemia in patients neighboring those treated with a probiotic preparation of the organism. J Clin Microbiol. 2003. PubMed 14605200 · doi:10.1128/JCM.41.11.5340-5343.2003