What Is Saccharomyces Boulardii?

A Yeast That May Help With Digestion, Diarrhea, and More

Saccharomyces Boulardii capsules

Verywell / Anastasia Tretiak

Saccharomyces boulardii (S. boulardii) is a probiotic yeast that is a variety of Saccharomyces cerevisiae (also known as baker’s yeast or brewer’s yeast). It has been isolated from lychee and mangosteen fruit.

The probiotic activity of S. boulardii ranges from improving gut barrier function, eradicating pathogens, producing antimicrobial peptides, stimulating the immune system, and inhibiting inflammation. Specifically, S. boulardii is used for the prevention and treatment of gastrointestinal tract disorders including diarrhea symptoms.

This article discusses the uses, side effects, and precautions of S. boulardii. It also covers what to look for in an S. boulardii supplement.

Dietary supplements are not regulated like drugs in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. When possible, choose a supplement that has been tested by a trusted third party, such as USP, ConsumerLabs, or NSF.

However, even if supplements are third-party tested, that doesn’t mean they are necessarily safe for all or effective in general. Therefore, it is important to talk to your healthcare provider about any supplements you plan to take and to check in about any potential interactions with other supplements or medications.

Supplement Facts

  • Active ingredient(s): Saccharomyces Boulardii
  • Alternate name(s): Yeast probiotic
  • Legal status: Over-the-counter dietary supplement (United States)
  • Suggested dose: The optimal dose for S. boulardii has not been established; doses used in clinical trials tend to be 250 to 500 milligrams (mg) per day in children and not more than 1000 milligrams (mg) per day in adults.
  • Safety considerations: Pregnancy, breastfeeding, children, older adults, those with digestive tract disease and weakened immune systems, and yeast allergies. Common side effects: bloating, flatulence. Rare but serious side effect: fungal blood infection (in people with multiple serious medical conditions or central venous catheters).

Uses of Saccharomyces Boulardii

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Saccharomyces boulardii is commonly used for gastrointestinal disorders such as the following:

Other uses of S. boulardii include the following:

Traveler’s Diarrhea

A randomized study of traveling individuals used either 250 or 500 milligrams (mg) per day of S. boulardii or a placebo for three weeks. The product was given five days before the trip and continued throughout. In the placebo group, 43% developed TD. However, in the low-dose S. boulardii, 34% developed TD. And in the higher-dose S. boulardii group, 32% developed TD. So treatment with S.boulardii lowered development of TD by around 10% in these groups. A limitation of the study was that it was conducted on people from Austria and thus may not be generalizable to other populations.

In a similar study of 3000 travelers, S. boulardii was shown to reduce the incidence of TD dose-dependently (the outcome depended on the dose). Specifically, 39% in the placebo group, 34% in the group given a lower dose of S. boulardii, and 29% in the group given a higher dose of S. boulardii developed TD. However, the study was limited because only 34%  of the participants completed the study.

Antibiotic-Associated Diarrhea

A systematic review (a collection of studies) showed that S. boulardii reduced the risk of AAD in people treated with antibiotics from 18.7% to 8.5% compared with placebo or no treatment. The risk of AAD decreased in both adults and children. However, one limitation was that the quality of the included trials varied. More studies may be needed.

Irritable Bowel Syndrome (IBS)

A study of people with irritable bowel syndrome (IBS) used S. boulardii (9 billion colony-forming units, or CFU, per day) or a placebo for four weeks. The daily number of stools in the S. boulardii group decreased, and 87.5% of this group reported improvement in IBS symptoms compared with 72% of the placebo group. However, the sample size of the study was small.

Crohn’s Disease

A randomized, double-blinded trial conducted on 34 people aged from 19 to 54 years with Crohn’s disease in remission showed that after three months, the S. boulardii group improved the gut barrier function compared to the placebo group. However, the study was limited due to its small sample size.

Ulcerative Colitis

A study assessed the efficacy of adding S. boulardii in adults with mild-to-moderate clinical flare-ups of ulcerative colitis. The dosage was 250 milligrams (mg) by mouth three times a day for four weeks. S. boulardii was used in addition to maintenance treatment with Lialda (mesalamine). Over half of the participants attained clinical remission. Further studies with higher sample sizes are needed to confirm the result. 

What Are the Side Effects of Saccharomyces Boulardii?

Your provider may recommend you take S. boulardii for certain gastrointestinal conditions. However, consuming a supplement like S. boulardii may have potential side effects. These side effects may be common or severe.

Common Side Effects

No side effects were noted by travelers in studies assessing the effect of S. boulardii supplementation on TD. Likewise, no side effects were reported in studies using S. boulardii for AAD and IBS.

However, common side effects of S. boulardii include the following:

Severe Side Effects

Although infrequent, cases of fungemia (a condition marked by fungi in the blood) have been reported, particularly in those with severe comorbidities and those with central venous catheters.

Seek medical attention if you experience an allergic reaction to S. boulardii.


Caution should be taken if the following apply to you:

  • Pregnancy and breastfeeding: Due to insufficient safety information on using S. boulardii when pregnant or breastfeeding, S. boulardii should be avoided. 
  • Children: A healthcare provider should evaluate diarrhea in children before using S. boulardiiSaccharomyces boulardii supplementation has reduced the duration and severity of diarrhea in children with acute diarrhea.
  • Older adults: Due to the increased risk of fungal infection, older adults should avoid using S. boulardii
  • Digestive tract disease: S. boulardii has caused fungal infections in people with digestive tract diseases; please consult your healthcare provider before starting S. boulardii
  • Weakened immune system: Saccharomyces boulardii has caused fungal infections due to catheter contamination in people with a weakened immune system. Please consult your healthcare provider before starting S. boulardii
  • Yeast allergy: Avoid S. boulardii if you have a yeast allergy.

Dosage: How Much Saccharomyces Boulardii Should I Take?

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

Listed below are the doses of S. boulardii used in clinical trials for various conditions: 

  • Traveler’s Diarrhea: Doses of 250, 500, or 1000 milligrams (mg) capsules taken by mouth per day for three weeks in adults.
  • Antibiotic-Associated Diarrhea: Not less than 250 mg (5 billion CFU) but not more than 500 mg (10 billion CFU) in children and not more than 1000 mg (20 billion CFU) in adults.
  • Irritable Bowel Syndrome: An S. boulardii dose of 9 billion CFU taken by mouth per day was used for four weeks in adults with IBS.
  • Crohn’s disease: For adults with Crohn’s disease, an S. boulardii dose of 500 milligrams (mg), two capsules taken by mouth per day for up to six months, was used in addition to maintenance therapy with mesalamine.
  • Ulcerative colitis: For adults with ulcerative colitis, 250 milligrams (mg) of S. boulardii was taken by mouth three times a day for four weeks during maintenance treatment with mesalamine.

What Happens If I Take Too Much Saccharomyces Boulardii?

In general, the daily dose of S. boulardii is typically greater than 1 billion per day (but no more than 20 billion CFU per day in adults for AAD), and the duration of treatment ranges from seven days to six months.

Unlike other probiotics derived from bacterial strains, S. boulardii has not developed any antibiotic or antifungal resistance.

Moreover, human studies indicated that S. boulardii does not persist in the intestines three to five days after oral (by mouth), and ingestion is discontinued.


Saccharomyces boulardii is a yeast and fungus. Therefore, taking antifungal medications with S. boulardii can reduce its effects. If an antifungal medication needs to be taken concurrently with S. boulardii, it is suggested that the two be separated by at least four hours apart.

It is essential to carefully read a supplement's ingredient list and nutrition facts panel to know which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications. 

How to Store Saccharomyces Boulardii

Some S. boulardii products are stored at room temperature, while others are stored in the refrigerator. Follow the directions on the product label. Discard per packaging instructions.

Similar Supplements

In addition to S. boulardii, here are some examples of other probiotic supplements:

Similar to S. boulardii, the aforementioned probiotics are used for AAD, IBS, TD, and ulcerative colitis. Specifically, Bacillus coagulans, bifidobacterium (B. bifidum, B. breve, and B. longum), and lactobacillus (L. acidophilus, L. casei, L. plantarum,  and L. rhamnosus) are used for AAD.

For IBS, B. bifidum, B. breve, and B. longum and L. acidophilus, L. plantarum, and L. rhamnosus have been shown to be effective.

Bifidobacterium breve, L. acidophilus, and L. rhamnosus have also been shown to be effective for TD and ulcerative colitis.

Frequently Asked Questions

  • When do I take an S. boulardii supplement to help prevent antibiotic-associated diarrhea (AAD)?

    To prevent AAD, S. boulardii should be started early in the course of antibiotic treatment before the change in the gut flora occurs. In clinical trials, S. boulardii is continued for the duration of antibiotic treatment. However, it is unclear whether prolonged use of S. boulardii would be necessary.

  • Why are some S. boulardii supplements stored at room temperature while others are stored in the refrigerator?

    Saccharomyces boulardii can be in either the lyophilized (freeze-dried) or heat-dried forms.

    Whereas freeze-dried products are stable at room temperature and thus are stored at room temperature, heat-dried products are unstable at room temperature and thus must be refrigerated.

  • How is S. boulardii different from other probiotic strains?

    Due to its natural fungal properties, S. boulardii cannot promote the spread of antimicrobial resistance. On the other hand, bacterial probiotics can contribute to antimicrobial resistance.

    Other differences between yeast probiotics and bacterial probiotics exist. For example, bacterial probiotics should be taken separately from antibiotics by at least two hours.

    However, yeast probiotics do not need to be taken separately from antibiotics because they are intrinsically resistant to antibiotics.

Sources of Saccharomyces Boulardii & What To Look For

Saccharomyces boulardii is available as a supplement or in liquid beverages along with other probiotics.

The quality and efficacy of probiotic supplements vary from product to product even if the label states that it contains S. boulardii due to the lower than stated dose or inaccurate strain composition.

Furthermore, a systematic review suggested finding a probiotic product in which the manufacturing company has sponsored original clinical trials. Such a product indicates a degree of commitment that may be absent in other companies that do not sponsor original research.

Food Sources of Saccharomyces Boulardii

Saccharomyces boulardii, in combination with other probiotics, can be found in kombucha fermented tea.

Not only can S. boulardii be derived from lychee, mangosteen fruit, and kombucha, but it is also derived from dairy products such as kefir.

Saccharomyces Boulardii Supplements

Saccharomyces boulardii is available in capsules of either lyophilized (freeze-dried) or heat-dried preparations. 

The potency or shelf-life of the probiotic product depends on how it is manufactured. For example, heat-dried products, which lose their potency rapidly,  should be refrigerated after opening. Conversely, freeze-dried products of S. boulardii are stable at room temperature, provided they are protected from moisture.


Saccharomyces boulardii is a yeast probiotic clinically studied for gastrointestinal disorders, including traveler’s diarrhea, antibiotitc-associated diarrhea, irritable bowel syndrome, Crohn’s disease, and ulcerative colitis. 

In general, S. boulardii is well-tolerated, but common side effects include bloating, flatulence, and constipation. People with a weakened immune system or who have central venous catheters should not use S. boulardii due to the risk of fungal infection in the blood. 

It would help if you talked with your healthcare provider before taking S. boulardii to ensure it is safe. Tell them about any other conditions and symptoms you have, or medications you take.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lazo-Vélez MA, Serna-Saldívar SO, Rosales-Medina MF, Tinoco-Alvear M, Briones-García M. Application of Saccharomyces cerevisiae var. boulardii in food processing: a review. J Appl Microbiol. 2018;125(4):943-951. doi:10.1111/jam.14037

  2. Ansari F, Alian Samakkhah S, Bahadori A, et al. Health-promoting properties of Saccharomyces cerevisiae var. boulardii as a probiotic; characteristics, isolation, and applications in dairy products [published online ahead of print, 2021 Jul 13]. Crit Rev Food Sci Nutr. 2021;1-29. doi:10.1080/10408398.2021.1949577

  3. Pais P, Almeida V, Yılmaz M, Teixeira MC. Saccharomyces boulardii: What Makes It Tick as Successful Probiotic?. J Fungi (Basel). 2020;6(2):78. Published 2020 Jun 4. doi:10.3390/jof6020078

  4. Szajewska 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

  5. MedlinePlus. Saccharomyces Boulardii.

  6. Williams NT. Probiotics. Am J Health Syst Pharm. 2010;67(6):449-458. doi:10.2146/ajhp090168

  7. McFarland LV. Systematic review and meta-analysis of Saccharomyces boulardii in adult patients. World J Gastroenterol. 2010;16(18):2202-2222. doi:10.3748/wjg.v16.i18.2202

  8. Ryan JJ, Hanes DA, Schafer MB, Mikolai J, Zwickey H. Effect of the Probiotic Saccharomyces boulardii on Cholesterol and Lipoprotein Particles in Hypercholesterolemic Adults: A Single-Arm, Open-Label Pilot Study. J Altern Complement Med. 2015;21(5):288-293. doi:10.1089/acm.2014.0063

  9. Kaźmierczak-Siedlecka K, Ruszkowski J, Fic M, Folwarski M, Makarewicz W. Saccharomyces boulardii CNCM I-745: A Non-bacterial Microorganism Used as Probiotic Agent in Supporting Treatment of Selected Diseases. Curr Microbiol. 2020;77(9):1987-1996. doi:10.1007/s00284-020-02053-9

  10. Sivananthan K, Petersen AM. Review of Saccharomyces boulardii as a treatment option in IBD. Immunopharmacol Immunotoxicol. 2018;40(6):465-475. doi:10.1080/08923973.2018.1469143

  11. Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev. 2019;4(4):CD004827. Published 2019 Apr 30. doi:10.1002/14651858.CD004827.pub5

  12. Mourey F, Sureja V, Kheni D, et al. A Multicenter, Randomized, Double-blind, Placebo-controlled Trial of Saccharomyces boulardii in Infants and Children With Acute Diarrhea. Pediatr Infect Dis J. 2020;39(11):e347-e351. doi:10.1097/INF.0000000000002849

  13. Wilkins T, Sequoia J. Probiotics for Gastrointestinal Conditions: A Summary of the Evidence. Am Fam Physician. 2017;96(3):170-178.

By Trang Tran, PharmD
Trang Tran, PharmD, is a pharmacist who is passionate about integrative health. 

Originally written by Cathy Wong