The standard adult dose of Saccharomyces boulardii is 500 mg per day, typically split into two 250 mg doses. That said, the right amount depends on why you’re taking it. Doses in clinical trials range from 250 mg to 1,000 mg daily, with higher amounts reserved for more serious gut conditions.
Standard Adult Dose
For general digestive support and preventing antibiotic-related diarrhea, the well-studied dose is 250 mg twice daily (500 mg total). Most capsules on the market come in 250 mg, which translates to roughly 5 billion colony-forming units (CFU) per capsule, though this varies by brand. Some products combine the full 500 mg into a single capsule.
Children are typically given a lower amount. Pediatric studies have used 250 to 750 mg per day, depending on the child’s age and the condition being treated, with courses lasting 5 to 7 days for acute diarrhea. For kids, 250 mg once daily is the most common starting point.
Doses for Specific Conditions
Antibiotic-Associated Diarrhea
If you’re taking antibiotics and want to protect your gut, 250 mg twice daily is the dose with the strongest evidence. In a randomized, placebo-controlled trial of hospitalized patients in Germany, participants took 250 mg capsules twice daily starting within 24 hours of their first antibiotic dose. They continued for 7 days after finishing the antibiotic course. That timing matters: starting early and continuing after the antibiotic is done gives the yeast time to keep the gut stable during the most vulnerable window.
C. difficile Recurrence
For people dealing with recurrent C. difficile infections, a higher dose of 1,000 mg per day (two 250 mg capsules, twice daily) has been studied alongside antibiotic treatment. In one trial published in Clinical Infectious Diseases, patients who took 1 g/day of S. boulardii for 28 days while on high-dose vancomycin had a recurrence rate of just 16.7%, compared to 50% in the placebo group. That’s a meaningful difference, but this protocol was used under medical supervision, not as a standalone supplement.
Traveler’s Diarrhea
You may have heard S. boulardii recommended before international trips. The CDC’s current position, however, is that evidence for using any probiotic to prevent traveler’s diarrhea is inconclusive. Small studies exist, but standardized preparations aren’t reliably available across markets, making it hard to draw firm conclusions. If you do decide to try it, the general 500 mg/day dose is what most practitioners suggest.
When and How to Take It
S. boulardii is a yeast, not a bacteria, which gives it a practical advantage: it’s naturally more resistant to stomach acid than most bacterial probiotics. It arrives in your intestines in a dormant, hardy form that survives the acidic environment of your stomach better than strains like Lactobacillus.
That resilience means timing is less critical than it is for bacterial probiotics, but taking it with breakfast is still a reasonable approach. Your bowels are more active when you’re moving around during the day, which helps the yeast travel from your stomach to your colon where it does its work. Pairing it with a meal that includes some protein, fat, and carbohydrates can further buffer stomach acid and support survival. If you’re taking it twice daily, morning and evening with meals is a simple routine.
One important note if you’re using it alongside antibiotics: S. boulardii is not killed by antibacterial drugs because it’s a yeast, not a bacterium. You can take them at the same time without worrying that the antibiotic will destroy the probiotic, which is not the case with bacterial strains.
Upper Limits and Safety
There is no formally established upper limit for S. boulardii. Clinical trials have used doses up to 1,000 mg per day for 28 days without reporting adverse effects in otherwise healthy people. A review in Therapeutic Advances in Gastroenterology noted that no adverse effects were observed in any of the clinical trials conducted with S. boulardii. For most people, the 250 to 500 mg range is sufficient, and going higher provides diminishing returns unless you’re managing a specific condition like C. difficile recurrence.
The safety picture changes significantly for certain groups. S. boulardii fungemia, where the yeast enters the bloodstream, has been documented in nearly 100 cases, almost exclusively in people who are immunocompromised, critically ill, or have central venous catheters. The yeast can colonize catheter surfaces and enter the blood that way. Premature infants, people with short-gut syndrome, and anyone with a weakened immune system should avoid S. boulardii entirely. In immunocompetent (healthy immune system) individuals, fungemia has not been reported.
Mild side effects like gas or bloating can occur when starting any probiotic but typically resolve within a few days. A rare allergic gut reaction has been documented in an infant with a prior food protein sensitivity, but this is an unusual case.
How Long to Take It
The duration depends on your reason for using it. For acute diarrhea in children, 5 to 7 days is the studied course. For antibiotic-associated diarrhea prevention, the evidence supports taking it for the full length of your antibiotic course plus 7 additional days afterward. For C. difficile recurrence prevention, the studied duration is 28 days.
If you’re taking S. boulardii as an ongoing digestive supplement without a specific medical reason, there’s no established maximum duration. Long-term use hasn’t raised safety concerns in healthy adults, but the strongest clinical evidence is for short, targeted courses tied to a specific gut disruption rather than indefinite daily use.