250–500 mg, 1–2 times a day.
Prevents antibiotic-associated diarrhea.
View the study (RCT) →Shortens the duration of acute diarrhea.
View the study (meta-analysis) →⏱ 3 min read
Saccharomyces boulardii is a peculiar probiotic yeast among the microorganisms marketed as probiotics: unlike most (bifidobacteria, lactobacilli), it is not a bacterium but a fungus, specifically a strain of Saccharomyces cerevisiae with particular properties, discovered in the 1920s on tropical fruits by the French microbiologist Henri Boulard during a cholera epidemic in Indochina; the initial observation was that local inhabitants who drank infusions made with litchi bark (in which S. boulardii is naturally present) had less diarrhea during the outbreak.
The pharmacological properties that distinguish S. boulardii from classic bacterial probiotics are three and highly relevant clinically: intrinsic resistance to antibacterial antibiotics (being a fungus, it is not affected by antibiotics such as amoxicillin, clarithromycin, ciprofloxacin, and the like), the ability to survive gastric acid pH without needing an enteric coating, and an optimal growth temperature (37°C) that coincides exactly with human body temperature; these characteristics allow it to colonize the intestine transiently during simultaneous antibiotic use, a property that no bacterial probiotic can offer.
The indication with the best clinical evidence is the prevention of antibiotic-associated diarrhea: multiple meta-analyses have confirmed that S. boulardii at doses of 250-1,000 milligrams daily significantly reduces the incidence of antibiotic-associated diarrhea in adults and children, with numbers needed to treat (NNT) between 9 and 13 (that is, for every 9-13 people treated during the antibiotic course, one episode of diarrhea is prevented).
A meta-analysis published in Aliment Pharmacol Ther in 2015 with 21 trials confirmed reductions of 50-60 percent in the incidence of antibiotic-associated diarrhea, an effect size that is clinically very relevant and comes with an excellent safety profile, which has led several clinical guidelines to include S. boulardii as a specific recommendation when prescribing broad-spectrum antibiotics, especially in people with risk factors.
In preventing recurrence of Clostridium difficile infection (a major cause of recurrent hospital-acquired colitis), several trials have shown significant reductions in recurrence with supplementation for 4 weeks in people with previous episodes of the infection, a recognized indication with solid clinical data, although somewhat less consistent than for the general prevention of antibiotic-associated diarrhea.
In acute diarrhea in children, several pediatric trials have shown a significant reduction in the duration of the diarrheal episode and in the number of stools with supplementation at 250-500 mg/day for 5 days, an indication supported by European pediatric guidelines as an adjunct treatment to oral rehydration.
In traveler's diarrhea, several small studies have shown reductions in incidence with prophylactic supplementation started before the trip and continued throughout the stay; in ulcerative colitis and inflammatory bowel disease, the data are more limited but point to modest symptomatic improvements as an adjunct to standard treatment.
The doses studied are 250-1,000 milligrams daily (5 billion to 20 billion CFU), divided into one or two doses; to prevent antibiotic-associated diarrhea, start on the same day as the antibiotic and continue for 7-14 days after finishing it; for acute diarrhea, for 5-7 days; for preventing C. difficile recurrence, 4 weeks at high doses; typical commercial products contain freeze-dried S. boulardii in capsules or sachets that are stable at room temperature.
Generally very well tolerated with an excellent safety profile; the adverse effects described are rare (mild digestive discomfort, transient flatulence, occasionally thirst from the osmotic effect); the most important clinical consideration is the sporadic reports of fungemia (systemic invasion) in critically ill immunocompromised patients, especially with central venous catheters, which justifies avoiding S. boulardii in critically hospitalized people, in people with severe immunodeficiencies, with central venous catheters, or with prosthetic heart valves; most of the general population can use it with confidence; in pregnancy and breastfeeding it is considered safe, although consulting a clinician is advisable; in pediatrics it is the probiotic option with the best clinical profile for acute diarrhea and antibiotic-associated prevention.
Information, not medical advice. Scientific evidence reflects the quality of the studies.