What This Strain Does
Saccharomyces boulardii stands uniquely apart from other probiotics because it is not a bacterium at all—it is a beneficial yeast. Discovered in 1923 by French scientist Henri Boulard, who observed Southeast Asian natives chewing on lychee and mangosteen skins during cholera outbreaks, this probiotic yeast has become one of the most clinically validated interventions for diarrhea prevention and treatment worldwide.
Unlike bacterial probiotics, S. boulardii offers several distinct advantages rooted in its fungal nature. It cannot be killed by antibiotics, making it an ideal companion during antibiotic therapy when other beneficial bacteria are being eliminated. This yeast maintains its efficacy regardless of what antibacterial medications you may be taking, continuing to provide gut protection when you need it most.
S. boulardii works through multiple mechanisms to protect and restore gut health. It produces enzymes that neutralize bacterial toxins, particularly those released by Clostridium difficile (C. diff). The yeast also secretes factors that support the intestinal barrier, reduce inflammation, and stimulate the production of secretory immunoglobulin A (sIgA), an important antibody for gut immunity. Additionally, S. boulardii competes with pathogenic organisms for binding sites and nutrients, effectively crowding out harmful invaders.
One remarkable characteristic of S. boulardii is that it does not permanently colonize the gut. It establishes a temporary but therapeutically beneficial presence, typically clearing from the system within 3-5 days after discontinuation. This transient nature makes it exceptionally safe for short-term therapeutic use while still providing robust protection during vulnerable periods.
Research Highlights
The clinical evidence supporting S. boulardii is extensive and compelling, with hundreds of studies conducted over several decades. Here are some of the most significant findings:
Antibiotic-Associated Diarrhea Prevention: A landmark meta-analysis published in the World Journal of Gastroenterology examined 21 randomized controlled trials involving over 4,700 patients. The analysis found that S. boulardii reduced the risk of antibiotic-associated diarrhea by 53% compared to placebo. This protective effect was consistent across different types of antibiotics and patient populations.
Clostridium difficile Infection: Research published in the Journal of Clinical Gastroenterology demonstrated that S. boulardii, when combined with standard antibiotic treatment, reduced C. diff recurrence rates by approximately 50%. For patients who have experienced C. diff infection, which can be life-threatening in severe cases, this represents a significant clinical benefit.
Traveler’s Diarrhea: A study of over 1,000 travelers found that those taking S. boulardii experienced significantly lower rates of traveler’s diarrhea compared to the control group. The protective effect was most pronounced during travel to high-risk destinations and among those who had experienced travel-related digestive issues previously.
Inflammatory Bowel Disease: Clinical trials in patients with Crohn’s disease and ulcerative colitis have shown that S. boulardii supplementation can help maintain remission and reduce disease activity scores. A study in the American Journal of Gastroenterology found that Crohn’s patients taking S. boulardii in addition to standard therapy had significantly lower relapse rates over a 6-month period.
Specific Strains to Look For
While S. boulardii is technically a single species, products may use different designations that can cause confusion. Here is what you need to know:
S. boulardii CNCM I-745 (also known as S. boulardii lyo) is the most extensively researched strain, with over 100 clinical trials supporting its efficacy. This is the strain found in the original French pharmaceutical product Florastor and its equivalents worldwide.
S. boulardii HANSEN CBS 5926 is another well-documented strain used in various probiotic formulations, with demonstrated efficacy in clinical settings.
Some products may list S. cerevisiae var. boulardii or simply S. cerevisiae boulardii. Taxonomically, S. boulardii is closely related to baker’s yeast (S. cerevisiae), and some classification systems consider it a subspecies. However, its therapeutic properties are distinct, so ensure the product specifically identifies boulardii rather than generic S. cerevisiae.
What to Look For in Products
When selecting a Saccharomyces boulardii supplement, consider the following factors:
CFU Count: Most clinical studies used doses between 250 mg and 500 mg daily, typically providing 5-10 billion CFU. Some conditions may benefit from higher doses up to 1,000 mg daily.
Formulation: S. boulardii is available in capsules, sachets, and powder forms. Capsules are most convenient for adults, while sachets or powder can be mixed into foods or beverages for children or those who have difficulty swallowing pills.
Heat Stability: While S. boulardii is more heat-stable than many bacterial probiotics, it still benefits from proper storage. Look for products with clear storage instructions and expiration dates.
Single Strain vs. Combination: For targeted diarrhea prevention or antibiotic support, single-strain S. boulardii products are highly effective. However, combination products with bacterial strains can provide broader gut support for general digestive wellness.
Quality Certifications: Choose products from reputable manufacturers with third-party testing, GMP certification, and clear labeling of the specific strain used.
Potential Side Effects
S. boulardii has an excellent safety profile established through decades of clinical use and research. Most people tolerate it well, but some may experience:
Gas and bloating: Initial use may cause temporary digestive discomfort as the gut microbiome adjusts. This typically resolves within a few days.
Thirst: Some users report increased thirst, which can be addressed by staying well-hydrated.
Constipation: Occasionally reported, particularly at higher doses.
Important Contraindication: S. boulardii should be avoided by individuals who are severely immunocompromised, have central venous catheters, or are critically ill. In rare cases, the yeast can enter the bloodstream (fungemia) in these vulnerable populations. If you have a compromised immune system, consult your healthcare provider before use.
Those with yeast allergies should exercise caution, though S. boulardii is generally distinct from allergenic yeasts in bread and beer.
How to Take
For Antibiotic-Associated Diarrhea Prevention: Begin taking S. boulardii on the first day of antibiotic treatment. Take 250-500 mg (5-10 billion CFU) twice daily, at least 2 hours apart from antibiotic doses if possible. Continue for 2-3 days after completing the antibiotic course.
For Traveler’s Diarrhea Prevention: Start supplementation 5-7 days before travel. Take 250-500 mg daily throughout the trip and for several days after returning home.
For Acute Diarrhea Treatment: Take 500 mg twice daily until symptoms resolve, typically 3-7 days. Maintain adequate hydration and seek medical attention if symptoms are severe or persistent.
For Inflammatory Bowel Disease Support: Work with your gastroenterologist to determine appropriate dosing, typically 500-1000 mg daily as an adjunct to standard therapy.
General Timing: S. boulardii can be taken with or without food. It is not destroyed by stomach acid and does not require food buffering like some bacterial probiotics.
Key Takeaways
- Unique probiotic yeast that survives antibiotic treatment, making it ideal for concurrent use with antibiotics
- Extensively researched with hundreds of clinical trials supporting its efficacy for diarrhea prevention and treatment
- Proven protection against antibiotic-associated diarrhea, C. diff infection, and traveler’s diarrhea
- Supports inflammatory bowel disease management as an adjunct to standard medical therapy
- Temporary colonization means it provides therapeutic benefits without permanently altering gut flora
- Excellent safety profile for most populations, though immunocompromised individuals should consult healthcare providers
- Does not require refrigeration making it convenient for travel and daily use
- Start early for best results—begin before antibiotic therapy or travel for preventive benefits