NOW's **Saccharomyces boulardii** delivers 10 billion CFU per capsule — a full daily dose of the probiotic yeast best known for preventing antibiotic-associated diarrhea. That single capsule already matches the top of the range used across the 100+ clinical trials behind it, so you don't need to stack capsules to reach an effective amount. Unlike bacterial probiotics, this yeast naturally shrugs off stomach acid and bile, so more of it survives the trip to your gut intact.

One thing worth knowing: the strongest evidence — the meta-analyses showing it roughly halves the risk of diarrhea during antibiotic courses — was built mostly on a specific reference strain (CNCM I-745). This product uses the closely related I-3799 strain, which shares the species' track record but hasn't been trialed as heavily on its own. It also needs refrigeration — keep it cold so the live cells survive to do their job.