Saccharomyces Boulardii

A probiotic yeast with the best evidence for preventing antibiotic-associated and traveler's diarrhea.

Overall grade: Grade B
Last revised: Jul 10, 2026; 2
graded outcomes: 0
references listed

A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.

2 at grade B — 2 graded rows

What is known

Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.

Outcome	Grade	Effect size	Agreement
Antibiotic-associated diarrheaWell supported	Evidence grade B	Moderate	high
Traveler's / acute diarrheaReduced	Evidence grade B	Moderate	mixed

Antibiotic-associated diarrheaEvidence grade B
Well supported
Moderatehigh
Traveler's / acute diarrheaEvidence grade B
Reduced
Moderatemixed

What is uncertain

Read off the same rows as above. Nothing here is added that the entry does not itself record.

Studies disagree: Traveler's / acute diarrhea (mixed agreement).

Interactions

Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.

AntibioticsMind the timing
Survives antibiotics (a yeast) — take through the course.

The evidence in words

What it is

S. boulardii is a probiotic yeast (not a bacterium), so antibiotics don't kill it.

How it works

It antagonizes pathogens, neutralizes toxins (including C. difficile toxins), and supports gut-barrier function.

What the evidence shows

Among the best-evidenced probiotics: it reduces antibiotic-associated diarrhea, helps prevent C. difficile recurrence and traveler's diarrhea, and shortens acute pediatric diarrhea. Strain-specific and reliable.

Safety & interactions

Safe for most; avoid in the critically ill or central-line patients (rare fungemia). antibiotics — Survives antibiotics (a yeast) — take through the course.

Bottom line

The go-to probiotic around antibiotics and for diarrhea prevention — being a yeast, it survives the antibiotic. Strong evidence.

Entries that share this one's tags or conditions.

Akkermansia muciniphilaA next-generation gut bacterium linked to metabolic health — one promising human trial, a lot still unknown.Evidence grade C
ProbioticsStrain-specific or nothing — real benefits for antibiotic-associated diarrhea and some IBS, but 'contains 40 billion CFU' is not a mechanism.Evidence grade B
Saccharomyces Boulardii for Antibiotic-associated diarrheaEvidence grade B — Well supportedEvidence grade B
Saccharomyces Boulardii for Traveler's / acute diarrheaEvidence grade B — ReducedEvidence grade B

Sources

This entry lists no references of its own.

Last revised Jul 10, 2026. A grade is this entry's reading of the evidence, not medical advice.