Saccharomyces boulardii CNCM I-745

Imagine your gut as a busy city with its own ecosystem of residents — millions of beneficial bacteria keeping things running smoothly. When you take antibiotics, it's a bit like a city-wide blackout: the good residents get wiped out right alongside the bad ones, leaving a vacuum that opportunistic troublemakers rush in to fill. That's where Saccharomyces boulardii CNCM I-745 comes in. This probiotic yeast was first isolated from tropical lychee and mangosteen fruit in the 1920s and has since become one of the most-studied probiotics on Earth. Because it's a yeast (a fungus), not a bacterium, antibiotics simply cannot touch it — making it the rare probiotic you can genuinely take alongside your antibiotic prescription without losing any of its benefits. Once it arrives in your gut, it acts like a security team and a cleanup crew combined: it physically binds to harmful pathogens and their toxins, helps rebuild the protective lining of the intestine, and sends calm-down signals to an overactive immune response — essentially restoring order to the city as fast as possible.

The conditions this strain has been most rigorously studied for tell a clear story: this is a probiotic built for gut emergencies. People taking a course of antibiotics — for anything from a sinus infection to a dental procedure — often experience loose, urgent diarrhea as a side effect. Clinical studies consistently show that taking this yeast probiotic alongside antibiotics dramatically cuts the risk of that happening; in some real-world studies, those who took it were far more likely to be free of diarrhea at follow-up compared to those who didn't. For people who have traveled abroad and come back with what's commonly known as traveler's diarrhea, this strain is one of the top evidence-backed choices recommended in international guidelines. It's also studied as a supportive tool for people dealing with Clostridioides difficile (C. diff) — a stubborn, sometimes dangerous infection that often flares up after antibiotic use. In children, the evidence is particularly impressive: multiple large-scale analyses of clinical trials show it shortens the duration of acute gastroenteritis (stomach bugs) by over a day and reduces hospital stays — results that have led major pediatric health organizations in Europe to formally recommend it. Beyond acute gut crises, it also shows real promise for people with diarrhea-predominant IBS and small intestinal bacterial overgrowth, where it helps restore a healthier balance of gut bacteria and reduce uncomfortable bloating and irregular bathroom habits.

One of the standout features of this strain is how well-tolerated it is across the board — in children from infancy upward, in the elderly, and in adults managing chronic digestive conditions. It moves through the gut without permanently colonizing it, meaning it does its work and then clears out naturally, which also makes it very unlikely to disrupt a healthy microbiome. The typical supplementation period aligns with whatever is triggering the disruption: for antibiotic courses, it's taken for the duration of antibiotics plus a few days after; for traveler's diarrhea prevention, it's started a few days before departure and continued throughout the trip. One critical safety note: people who are immunocompromised, have central venous catheters, or are critically ill should consult a physician before using any live probiotic, as there are rare reports of yeast entering the bloodstream in very vulnerable patients. For the vast majority of healthy people and children, however, this strain has an excellent safety record backed by decades of clinical use. As a bonus, emerging research suggests it may also help protect the gut lining when taking common pain relievers like NSAIDs, support Helicobacter pylori eradication therapy by reducing side effects, and even help reduce the spread of antibiotic resistance genes in the gut — adding new dimensions to an already impressive clinical profile.