Saccharomyces boulardii: Uses, How It Works, and Safety Information

Overview

Saccharomyces boulardii is a probiotic yeast used to prevent and treat various types of diarrhea. Unlike bacterial probiotics, this yeast is naturally antibiotic-resistant, making it ideal for use during antibiotic treatment. Available as Florastor and other brands, it’s one of the most studied probiotics with strong evidence for preventing antibiotic-associated and traveler’s diarrhea.

What It’s Used For

Saccharomyces boulardii is used for:

• Antibiotic-associated diarrhea prevention — can take alongside antibiotics
• Traveler’s diarrhea — prevention and treatment
• Acute infectious diarrhea — shortens duration
• C. difficile infection prevention — during and after antibiotic use
• Recurrent C. difficile — adjunct to standard treatment
• General digestive support — maintaining gut balance

Why It’s Different from Bacterial Probiotics

Key advantages of yeast-based probiotic:

• Naturally resistant to all antibiotics
• Can take at same time as antibiotic doses
• Not affected by antibacterial medications
• Works through different mechanisms than bacteria

This matters because:

• Bacterial probiotics (like Lactobacillus) can be killed by antibiotics
• S. boulardii remains effective throughout antibiotic treatment
• No need to time doses hours apart from antibiotics
• Simplifies dosing schedule

How It Works

Saccharomyces boulardii protects the gut through several mechanisms:

Anti-toxin effects:

• Breaks down bacterial toxins
• Neutralizes C. difficile toxins A and B
• Reduces toxin-mediated damage

Barrier support:

• Enhances gut lining integrity
• Increases secretory IgA
• Supports mucus production

Antimicrobial actions:

• Competes with pathogens for binding sites
• Produces antimicrobial substances
• Creates unfavorable environment for harmful organisms

Immune modulation:

• Anti-inflammatory effects
• Supports balanced immune response
• Reduces inflammatory cytokines

Available Forms

Brand name products:

• Florastor (most common)
• Florastor Kids (pediatric)

Supplement forms:

• Capsules
• Powder packets
• Chewables (pediatric)

Typical strengths:

• 250 mg (approximately 5 billion CFU)
• 500 mg capsules
• Various CFU counts available

How to Use

General guidelines:

• Take as directed on product label
• Can take with or without food
• Can take at same time as antibiotics
• Consistency improves results

During antibiotic treatment:

• Start when antibiotics begin
• Continue 1-2 weeks after antibiotics finish
• No need to separate doses (unlike bacterial probiotics)

Storage:

• Most products are shelf-stable
• Store in cool, dry place
• Check expiration dates
• Avoid excessive heat

What to Expect

Timeline:

• Protection begins with first doses
• Benefits during antibiotic use are immediate (prevention)
• General effects may take 1-2 weeks to notice
• Does not permanently colonize — transient presence

Important to understand:

• S. boulardii doesn’t permanently establish in gut
• Works while you’re taking it
• Clears from system within 3-5 days of stopping
• Continued use needed for ongoing benefits

Safety Information

Generally very safe:

• Well-tolerated by most people
• Few side effects
• Extensive safety record
• Safe for most adults and children

Use with caution or avoid if:

• Severely immunocompromised
• Central venous catheter in place
• Critical illness/ICU patients
• History of fungal infections in bloodstream

Rare but serious:

• Fungemia (yeast in bloodstream) — almost exclusively in immunocompromised or those with central lines
• Do not open capsules near central venous catheters

Evidence Summary

Strong evidence for:

• Preventing antibiotic-associated diarrhea
• Reducing duration of acute diarrhea
• Preventing C. difficile-associated diarrhea
• Traveler’s diarrhea prevention

Moderate evidence for:

• Adjunct treatment for recurrent C. difficile
• H. pylori treatment support (with antibiotics)
• Reducing inflammation in IBD

Limited evidence for:

• IBS symptom relief
• General immune support

When to See a Doctor

Consult a healthcare provider if:

• Diarrhea persists more than a few days
• Signs of dehydration develop
• Fever accompanies digestive symptoms
• Blood in stool
• Severe abdominal pain
• You’re immunocompromised and considering probiotics
• Symptoms worsen while taking

Sources

• National Institutes of Health Office of Dietary Supplements. Probiotics. Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/. Accessed March 2026.
• National Institutes of Health Office of Dietary Supplements. Probiotics. Consumer Fact Sheet. https://ods.od.nih.gov/factsheets/Probiotics-Consumer/. Accessed March 2026.