Florastor is a capsule of the probiotic yeast Saccharomyces boulardii strain CNCM I-745, and it has real trial evidence behind it, mainly for preventing diarrhea during antibiotic treatment. Pooled trials cut the risk of antibiotic-associated diarrhea roughly in half, from 18.7% to 8.5%.[1] Evidence for preventing C. diff is weaker and mixed, and it is not a treatment for an infection.
This review covers what each Florastor claim rests on, the dose and cost per day, side effects, and the people who should skip it. For the organism itself, see our S. boulardii guide.
How we reviewed this
We read the manufacturer's FAQ and Dual Action product page in October 2026, the clinical trials and systematic reviews cited below, and the guideline comparisons for C. diff. We did not test the product hands-on.
We found no third-party lab report on the pages we retrieved. Prices are the manufacturer's October 2026 web prices and will change. This page has no affiliate links.
What is in Florastor, and what is the Florastor dosage?
Each Florastor capsule contains 250 mg of S. boulardii CNCM I-745, measured in milligrams rather than colony-forming units (CFU) because yeast cells are about ten times larger than bacterial cells.[2] The label directions for adults are 2 capsules, 1 to 2 times a day, swallowed with 4 oz of water or juice, with or without food.[2]
| Detail | What the manufacturer states (October 2026) |
|---|---|
| Strain | S. boulardii CNCM I-745, a yeast |
| Amount | 250 mg per capsule |
| Adult directions | 2 capsules, 1 to 2 times daily |
| Storage | Room temperature, not refrigerated |
| Diet | Vegetarian, not vegan (contains milk-derived lactose) |
| Minimum course | At least 2 weeks, or as advised by a clinician |
Florastor Kids and Florastor Baby (the infant products) come as sticks rather than capsules: 1 stick, 1 to 2 times daily, mixed into soft food or a cool drink.[2] Those two products contain corn, unlike the adult capsules.[2] Ask a pediatrician before giving any probiotic to an infant; see probiotics for infants and newborns.
The 250 mg capsule can be opened into soft food or a cool drink, but not a hot (above 122 F), carbonated or alcoholic one, and the mix should be taken within 30 minutes.[2] According to the manufacturer, the yeast is resistant to most common antibiotics, which is why it is used alongside them.[2]
Does Florastor prevent antibiotic-associated diarrhea?
Yes, this is its best-supported use. A 2015 meta-analysis of 21 randomized trials (4,780 people) found S. boulardii lowered antibiotic-associated diarrhea from 18.7% to 8.5% (relative risk 0.47; number needed to treat 10).[1] The result held in children (20.9% to 8.8%) and adults (17.4% to 8.2%).[1]
One of the child trials, in 269 children with ear or respiratory infections, gave 250 mg twice daily during antibiotics; 8% developed diarrhea versus 23% on placebo.[3] The AGA's technical review likewise found low-certainty evidence that this yeast may reduce C. diff-associated diarrhea in people on antibiotics (relative risk 0.41).[4]
Two caveats apply. Probiotic effects are strain-specific and condition-specific, so these results apply to this yeast and not to other probiotics.[5] And the Cochrane review in children found a dose effect for probiotics overall, with at least 5 billion CFU a day working better, and named S. boulardii as one of the high-dose candidates that needs confirmation in a large trial.[6]
Is Florastor good for C. diff?
It is an add-on at best, and only for people who have already had a recurrence. Guidelines do not endorse probiotics for preventing the infection, and the one major trial in people with active C. diff was small.
In the 1994 JAMA trial of 124 adults, 1 g a day of S. boulardii for four weeks alongside vancomycin or metronidazole cut recurrence in people with a history of recurrent disease (34.6% versus 64.7% on placebo). It showed no benefit after a first episode (19.3% versus 24.2%).[7] The AGA review graded that evidence low certainty.[4]
For prevention, the picture splits by who is taking antibiotics:
| Source | What it found or recommends |
|---|---|
| Cochrane 2025 (any probiotic, 38 trials, 13,179 people) | C. diff-associated diarrhea 1.6% versus 3.2% (relative risk 0.50, low certainty); about 65 people treated to prevent one case[8] |
| S. boulardii meta-analysis 2015 | Significant in children (relative risk 0.25), not in adults (0.8; 95% CI 0.47-1.34)[1] |
| ACG 2021 | Recommends against probiotics (conditional, moderate certainty)[9] |
| IDSA/SHEA 2021 | No recommendation[9] |
| ESCMID 2021 | Recommends against (strong, low certainty)[9] |
If you have, or suspect, C. diff (watery diarrhea after antibiotics, cramps, fever), you need a clinician and a prescribed treatment. See our C. difficile infection guide and the organism page for Clostridioides difficile.
Does Florastor help when you travel?
Modestly. A 2019 systematic review pooled six trials and found S. boulardii CNCM I-745 reduced traveler's diarrhea (relative risk 0.79; 95% CI 0.72-0.87), while Lactobacillus rhamnosus GG showed only a trend (p = 0.08) and Lactobacillus acidophilus showed no significant reduction.[10] The review notes the number of trials is still small.[10]
A relative risk of 0.79 means about a fifth fewer cases, not immunity. It does not replace careful food and water choices. Our traveler's diarrhea guide covers prevention and what to do if it starts.
Does Florastor help diarrhea in children, IBS or SIBO?
The evidence is thinner here.
- Children with acute gastroenteritis: a 2020 meta-analysis of 29 trials found S. boulardii shortened diarrhea by about one day (-1.06 days; 23 trials, 3,450 children) and hospital stays by 0.85 days, but the quality was low to very low and the trials varied a lot.[11]
- IBS-D with bacterial overgrowth: in one open-label pilot (54 enrolled, 48 analyzed, 15 days), people on the yeast plus diet advice had a larger drop in hydrogen breath output (41% versus 29%) and in symptom score (-134 versus -93) than diet advice alone.[12] It was small, unblinded and short, so treat it as a lead, not proof.
For the conditions themselves, see IBS, SIBO and our broader probiotics for diarrhea guide. If you are taking antibiotics for SIBO, ask the prescriber before adding any probiotic.
How does it work in the gut?
It does not move in permanently. The yeast peaks in stool within about 2 days of dosing and is cleared within 3 to 5 days of stopping.[13] While present, laboratory and animal work suggests it secretes a protease that breaks down C. difficile toxins A and B, raises antibody (IgA) responses, and helps keep the gut barrier intact.[13]
Most of that mechanism comes from lab and animal studies, so it explains why the yeast might work but does not prove it does in every person.[13]
What are the side effects of Florastor?
Most people have none or mild digestive effects. The manufacturer lists allergic reaction (skin rash) as a very rare effect.[2] Across probiotic trials, the common adverse events were gas, bloating, cramping, nausea and constipation, and the Cochrane review found adverse events were probably no more common than with placebo.[8][6]
The serious risk is rare but real: fungemia, a yeast infection of the bloodstream. A systematic review of 108 Saccharomyces fungemia cases found 67.6% occurred in people who had been given S. boulardii products, with ICU stays (31.5%) and tube or intravenous feeding (29.6%) the most common risk factors.[14] Reviews point to central venous catheters and contamination of the line by handling the product.[15][16]
Who should not take Florastor?
Skip it, or take it only on a clinician's say-so, if any of these apply:
- You have a central line, port, PICC or other open vascular access, or are in an intensive care setting.[2]
- You are severely immunocompromised, critically ill, or before or after an organ or bone marrow transplant.[2]
- You are allergic to yeast or any ingredient.[2]
- You are pregnant or nursing: the manufacturer says data are lacking and to consult a clinician first.[2]
Hospitalized patients are the group in whom the fungemia reports cluster.[14]
We did not find antifungal-interaction guidance on the manufacturer pages we retrieved. Because the product is a living yeast, ask a pharmacist before combining it with antifungal medicine. It is not a treatment for vaginal yeast infections; see probiotics for BV and yeast infections.
How much does Florastor cost per day?
At the manufacturer's October 2026 web prices for Dual Action, the larger bottles cost less per capsule.[17]
| Size | Price | Per capsule | Per day at 2 capsules | Per day at 4 capsules |
|---|---|---|---|---|
| 20 capsules | $19.82 | $0.99 | $1.98 | $3.96 |
| 30 capsules | $28.97 | $0.97 | $1.93 | $3.86 |
| 50 capsules | $39.99 | $0.80 | $1.60 | $3.20 |
| 100 capsules | $67.99 | $0.68 | $1.36 | $2.72 |
Per-day figures are our arithmetic from those prices. Retail prices and sale prices vary. The manufacturer also warns to buy on Amazon only when shipped and sold by Amazon or Biocodex USA, to avoid counterfeits.[2]
How does Florastor compare with other probiotics?
It is a different kind of product. Most probiotics are bacteria; this one is a yeast. For antibiotic-associated diarrhea, specific bacterial strains and combinations also have supporting trials, so the choice depends on the outcome you want and the strain printed on the label.[5][4]
Choose Florastor if you are on antibiotics and want a yeast that antibiotics will not kill. Consider a bacterial strain if you want support for something else, such as IBS or vaginal health. Our best probiotics overall and strain comparison pages compare options, and how long to take probiotics covers duration.
Bottom line
Florastor is a reasonable, well-studied option for preventing diarrhea while you take antibiotics, and a modest one for travel. It is not a C. diff treatment, and people with central lines, severe illness or weakened immunity should avoid it. Check the label for the strain name CNCM I-745 before you buy, and give it at least the manufacturer's suggested two weeks if you use it at all.
This article is for general educational purposes and is not medical advice. Product details were retrieved from the manufacturer's website in October 2026 and may change; the product was not tested by Biome Guide. Talk to a qualified healthcare professional before starting any probiotic, particularly if you are pregnant, immunocompromised, taking prescription medication, or managing a diagnosed condition.
Frequently Asked Questions
Is it okay to take Florastor every day?
The manufacturer says Florastor can be taken daily and recommends at least 2 weeks of use, because the yeast does not colonize the gut and is gone within about five days of the last dose. Most trials ran for the length of an antibiotic course plus a short follow-up, so long-term daily use is less well studied than short courses. If you plan to take it for months, ask a clinician, especially if you have a chronic condition.
Why do cardiologists warn against probiotics?
We did not find a cardiology guideline that warns against probiotics as a class. The documented risk for this yeast is bloodstream infection (fungemia), which is reported mainly in people with central venous catheters, intensive care stays, tube or intravenous feeding, or weakened immunity. If you have a central line or are critically ill, do not take it unless your care team says so.
What does Florastor do to your poop?
In trials, the yeast mostly firmed up loose stools: in a pilot trial of people with diarrhea-predominant IBS and bacterial overgrowth, 25.9% still had diarrhea after 15 days with it versus 47.6% without it. Gas, bloating and constipation are among the side effects reported across probiotic trials in general. If your stools get harder, lower the dose or stop and talk to a pharmacist.
Who are the three people who should not take probiotics?
There is no official list of three. For Florastor specifically, the manufacturer says to avoid it with a central line or port, in intensive care settings, before or after an organ or bone marrow transplant, if severely immunocompromised or critically ill, and if allergic to yeast. Systematic reviews of infections linked to this yeast point to the same groups.
What do gastroenterologists think of probiotics?
Opinion is split by condition and strain. For preventing diarrhea caused by antibiotics, systematic reviews are positive for this yeast. For preventing C. difficile infection, the 2021 ACG guideline recommends against probiotics, IDSA/SHEA makes no recommendation, and ESCMID recommends against them.
Can you take Florastor with antibiotics?
Yes. The manufacturer states the yeast is resistant to most common antibiotics, and preventing antibiotic-associated diarrhea is the best-studied use. Do not stop or change a prescribed antibiotic on your own; the yeast is an add-on, not a replacement.
What medications cannot be taken with probiotics?
We did not find a drug-interaction list on the manufacturer pages we retrieved. Florastor is a living yeast, so ask a pharmacist before combining it with antifungal drugs or with medicines that suppress the immune system. Antibiotics are not a problem: the manufacturer states the yeast is resistant to most common antibiotics, and pairing it with them is the best-studied use. Never stop a prescribed medicine to take a supplement.
Why shouldn't you take probiotics every day?
For most healthy adults there is no strong evidence that a daily probiotic is harmful, but the trials behind Florastor mostly followed people for days to weeks, so long-term daily use is less studied. The bigger concern is who takes it: people with central lines, critical illness or weakened immunity face a rare risk of bloodstream infection. If you are healthy and plan to use it for months, ask a clinician whether you need it.
How long does Florastor take to work?
The manufacturer recommends at least 2 weeks of use. In lab and human data the yeast reaches its peak level in the gut within about 2 days of dosing and is cleared from stool within 3 to 5 days of stopping, so any effect is tied to the days you take it.
References
- Szajewska H, Kołodziej M. Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea. Alimentary Pharmacology & Therapeutics. 2015;42(7):793-801. doi:10.1111/apt.13344 ↩
- Florastor. Frequently Asked Questions. florastor.com (manufacturer page, retrieved October 2026). 2026. Available at: https://florastor.com/a/faq ↩
- Kotowska M, Albrecht P, Szajewska H. Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea in children: a randomized double-blind placebo-controlled trial. Alimentary Pharmacology & Therapeutics. 2005;21(5):583-590. doi:10.1111/j.1365-2036.2005.02356.x ↩
- Preidis GA, Weizman AV, Kashyap PC, Morgan RL. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020;159(2):708-738.e4. doi:10.1053/j.gastro.2020.05.060 ↩
- McFarland LV, Evans CT, Goldstein EJC. Strain-specificity and disease-specificity of probiotic efficacy: a systematic review and meta-analysis. Frontiers in Medicine. 2018;5:124. doi:10.3389/fmed.2018.00124 ↩
- Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database of Systematic Reviews. 2019;4:CD004827. doi:10.1002/14651858.CD004827.pub5 ↩
- McFarland LV, Surawicz CM, Greenberg RN, et al.. A randomized placebo-controlled trial of Saccharomyces boulardii in combination with standard antibiotics for Clostridium difficile disease. JAMA. 1994;271(24):1913-1918. doi:10.1001/jama.1994.03510480037031 ↩
- Esmaeilinezhad Z, Ghosh NR, Walsh CM, et al.. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews. 2025;9:CD006095. doi:10.1002/14651858.CD006095.pub5 ↩
- Jones J, Pradhan A, Pizzuti ME, Bland CM, Bookstaver PB. Is Three Company or a Crowd? Comparing and Contrasting U.S. and European Clostridioides difficile Clinical Practice Guidelines. Antibiotics. 2022;11(9):1247. doi:10.3390/antibiotics11091247 ↩
- McFarland LV, Goh S. Are probiotics and prebiotics effective in the prevention of travellers' diarrhea: a systematic review and meta-analysis. Travel Medicine and Infectious Disease. 2019;27:11-19. doi:10.1016/j.tmaid.2018.09.007 ↩
- Szajewska H, Kołodziej M, Zalewski BM. Systematic review with meta-analysis: Saccharomyces boulardii for treating acute gastroenteritis in children - a 2020 update. Alimentary Pharmacology & Therapeutics. 2020;51(7):678-688. doi:10.1111/apt.15659 ↩
- Bustos Fernández LM, Man F, Lasa JS. Impact of Saccharomyces boulardii CNCM I-745 on bacterial overgrowth and composition of intestinal microbiota in diarrhea-predominant irritable bowel syndrome patients: results of a randomized pilot study. Digestive Diseases. 2023;41(5):798-809. doi:10.1159/000528954 ↩
- Terciolo C, Dapoigny M, Andre F. Beneficial effects of Saccharomyces boulardii CNCM I-745 on clinical disorders associated with intestinal barrier disruption. Clinical and Experimental Gastroenterology. 2019;12:67-82. doi:10.2147/CEG.S181590 ↩
- Vinayagamoorthy K, Pentapati KC, Prakash H. Epidemiology of Saccharomyces fungemia: a systematic review. Medical Mycology. 2023;61(2):myad014. doi:10.1093/mmy/myad014 ↩
- Kelesidis T, Pothoulakis C. Efficacy and safety of the probiotic Saccharomyces boulardii for the prevention and therapy of gastrointestinal disorders. Therapeutic Advances in Gastroenterology. 2011;5(2):111-125. doi:10.1177/1756283X11428502 ↩
- Whelan K, Myers CE. Safety of probiotics in patients receiving nutritional support: a systematic review of case reports, randomized controlled trials, and nonrandomized trials. The American Journal of Clinical Nutrition. 2010;91(3):687-703. doi:10.3945/ajcn.2009.28759 ↩
- Florastor. Florastor Dual Action Probiotic Supplement. florastor.com (manufacturer page, retrieved October 2026). 2026. Available at: https://florastor.com/products/florastor-dual-action-probiotic-supplement ↩