Saccharomyces boulardii

Can it prevent diarrhea during antibiotics?

A 2015 review of 21 randomized trials with 4,780 participants found less antibiotic-associated diarrhea: 8.5% with S. boulardii versus 18.7% in control groups. Both adult and pediatric analyses favored the yeast, although studies used different doses and settings. 1 2

The result is encouraging, but not universal. A later trial in 15 German hospitals found no preventive benefit among 477 adults and stopped early for futility. Diarrhea occurred in 21 of 246 yeast recipients and 19 of 231 placebo recipients. 1 2

What about an existing stomach bug?

NIH’s evidence summary reports that European pediatric guidance gives S. boulardii a weak recommendation for acute gastroenteritis, based on low-certainty evidence. US guidance is less favorable toward probiotics in this setting. A possible shorter illness should be weighed against that uncertainty. 3

Is it worth packing for a trip?

A strain-specific meta-analysis found a lower risk of travelers’ diarrhea with S. boulardii CNCM I-745, with a relative risk of 0.79. The number of relevant trials was limited. 4 5

Does it restore the microbiome or strengthen immunity?

A 12-week trial in 44 people with treated, virologically suppressed HIV found changes in selected gut bacteria alongside inflammatory markers. This is an interesting human signal that the yeast can influence the gut environment. 6 7