Best Saccharomyces Boulardii Supplements for Gut Health (2026)

S. boulardii is a non-pathogenic yeast originally isolated from lychee fruit. Because it's a yeast rather than a bacterium, it occupies a unique niche: it's completely resistant to antibiotics, which makes co-administration genuinely practical rather than just theoretically possible. In the gut, S. boulardii produces proteases that may degrade bacterial toxins, competes with pathogenic microorganisms for adhesion sites on intestinal epithelial cells, and appears to modulate secretory IgA production — a key component of mucosal immune defence. The CNCM I-745 strain has the most thoroughly characterised mechanism. It's been shown in human studies to influence the composition of the gut microbiota rather than simply passing through. The lyophilised form used by Florastor is also worth understanding: freeze-drying preserves the yeast cells in a dormant state that reactivates upon reaching the gut, which is why shelf stability is maintained without refrigeration. The '5 billion CFU equivalent' on lyophilised products reflects a conversion from the live cell count, though the two measurement systems aren't perfectly interchangeable.

The single most important factor when buying an S. boulardii supplement is strain designation. The CNCM I-745 strain is the strain used in the overwhelming majority of published human clinical trials. When a product doesn't specify this designation, you can't directly apply the clinical trial evidence to what you're buying. That's not necessarily a dealbreaker — plenty of S. boulardii products from reputable manufacturers without the CNCM I-745 designation still provide genuine support — but you should understand the distinction. CFU count is the second consideration. Most clinical trials in adults have used doses in the range of 5–10 billion CFU (or equivalent) per day. All three products on this list meet that threshold at one or two servings per day. What's less discussed is the lyophilised versus live organism question: Florastor uses a lyophilised form that lists '5 billion CFU equivalent' rather than live CFU, because the freeze-drying process changes how you measure viability. It's not a lesser product — it just uses a different metric that isn't perfectly comparable across brands. Shelf stability matters more than most people realise. S. boulardii is naturally more heat-tolerant than bacterial probiotics, and all products on this list are shelf-stable without refrigeration. For travellers especially, this is a practical advantage over lactobacillus-based probiotics that require a cold chain. That said, storing any probiotic away from direct heat and humidity extends viability throughout the container's shelf life. Finally, consider whether a prebiotic addition is relevant for you. Jarrow's MOS inclusion is genuinely differentiated — manno-oligosaccharides act as a substrate that may support the broader gut microbial community, not just the S. boulardii itself. If you're using S. boulardii specifically during antibiotic therapy, a prebiotic addition may be particularly valuable for recovery of the bacterial microbiome after the antibiotic course ends.