Saccharomyces boulardii

What it is

Saccharomyces boulardii is a beneficial yeast, a strain of Saccharomyces cerevisiae, first isolated from tropical fruit in the 1920s. Because it's a yeast rather than a bacterium, antibiotics don't kill it.

How it works

S. boulardii passes through the gut alive, where it appears to help keep the intestinal environment stable while antibiotics disrupt the usual bacteria. Lab and animal research suggests it may break down certain bacterial toxins, support the gut lining, and modulate local immune signals. Exactly which of these matter most in people isn't settled, but its resistance to antibiotics is a practical advantage over bacterial probiotics.

What it's been studied for

Commonly taken alongside antibiotics to reduce the chance of diarrhea, and for traveler's and infectious diarrhea.

What the evidence shows

Evidence is fairly strong for one use: meta-analyses of randomized trials found that taking S. boulardii alongside antibiotics lowered the risk of antibiotic-associated diarrhea in both children and adults, roughly by half in pooled analyses. Evidence for other uses, such as shortening infectious diarrhea in children or supporting C. difficile care alongside standard treatment, is more modest. The key limitation is that many trials were small or open-label, and benefits vary by strain and population.

Who should consider it

Otherwise healthy adults and children starting a course of antibiotics are the group with the clearest supporting evidence. People without a specific reason — for example, those looking for general gut wellness — probably won't notice much. People who are critically ill, significantly immunocompromised, or have a central line should not take it unless their physician recommends it.

Amounts commonly studied

Studies typically used 250 to 1,000 mg per day (roughly 5 to 20 billion cells), started with the antibiotic course and often continued for several days to a couple of weeks afterward.

How to take it

Studies typically started it on the first day of antibiotics and continued for the full course, often plus a few days to two weeks afterward. It can be taken with or without food and at the same time as antibiotics. Diarrhea with fever, blood, severe pain, or signs of dehydration — especially after antibiotics — needs medical attention rather than self-treatment, so talk to your provider.

Forms & absorption

Capsules and powder sachets are most common; it's a live organism, so follow storage directions. It can be taken at the same time as antibiotics, but antifungal medications can inactivate it.

Food sources

None — S. boulardii isn't present in meaningful amounts in everyday foods; it's taken as a supplement. Fermented foods contain other microbes, not this studied strain.

Safety & interactions

Generally well tolerated; bloating, gas, thirst, or constipation can occur. Rare but serious bloodstream yeast infections (fungemia) have been reported, mainly in critically ill or immunocompromised people and those with central venous catheters — people in these groups, and anyone caring for them who opens capsules nearby, should avoid it unless a physician directs otherwise. Antifungal drugs such as fluconazole or nystatin can reduce its effect, and people with yeast allergy should avoid it; data in pregnancy are limited.

Common questions

Can I take it at the same time as my antibiotic?

Yes. Because it's a yeast, antibiotics don't kill it, and trials typically gave it alongside the antibiotic. Antifungal medicines are a different story and can reduce its effect.

Is it safe for everyone?

For most healthy people, yes. The exception is people who are critically ill, immunocompromised, or have a central venous catheter, in whom rare bloodstream yeast infections have been reported — they should avoid it unless a physician says otherwise.

Is it the same as baker's yeast?

They're closely related, but S. boulardii is a distinct strain that was studied specifically as a probiotic. Baker's or brewer's yeast shouldn't be assumed to do the same thing.