Florastor calls itself “the last probiotic you’ll ever need.” Bold trademark. So I did what I always do: I dug through the clinical data, the fine print, and decades of research to see if that crown is earned or just expensive marketing. The whole pitch revolves around one strain—Saccharomyces boulardii CNCM I-745—and here’s the genuinely important part: it’s yeast-based, so antibiotics can’t kill it. When antibiotics wipe out your gut bacteria, Florastor can keep working where most bacterial probiotics tap out. But the story gets messy once you match the label to the studies. The research is strongest for specific protocols—antibiotic-associated diarrhea, traveler’s diarrhea, and C. difficile prevention. Meta-analysis data shows antibiotic-associated diarrhea risk dropping from 17.2% to 6.7, and a Harvard Beth Israel study backs microbiota protection during antibiotics. Meanwhile, the bottle leans hard into broad “daily wellness” and “immune health,” yet the published trials Florastor cites are overwhelmingly diarrhea-focused. Add in the “#1 selling” claim with a “reference on file” footnote, the FDA disclaimer asterisk on every claim, and lactose in the ingredient list, and yeah—this is a clinically validated specialist, not a magical daily gut reset for everyone. If you need it for the right job, it delivers. If you’re paying $40/month for vague immune optimization, the evidence is thinner than the label suggests.