Saccharomyces boulardii

What Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079) is and how it works

Saccharomyces boulardii is a probiotic ("friendly") yeast taken by mouth to help support or restore the normal balance of microorganisms in the gut, most often used to help reduce diarrhoea, including diarrhoea that can occur alongside antibiotic treatment. (2) (3) (1)

How this product is regulated is genuinely different from country to country -- in France it is a licensed medicine with its own product label; in the US and UK it is sold as a food/dietary supplement that has not been evaluated by the medicines regulator for safety or effectiveness in the way a licensed medicine is. Regardless of which category applies where you live, there is a real and serious safety issue to know about: rare but genuine cases of the yeast entering the bloodstream (fungaemia) have been reported in critically ill or immunocompromised patients, and in patients with a central line (central venous catheter) -- this product should not be used in those situations. Always tell your clinician you are taking (or considering) this product, especially if you are seriously unwell, immunocompromised, or have any kind of central line or catheter in place.

Mechanism of action: how Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079) works

Saccharomyces boulardii is a non-pathogenic probiotic yeast, taxonomically a strain of Saccharomyces cerevisiae, thought to act within the gut lumen to help normalise gut flora and reduce pathogen-associated diarrhoea; it is not systemically absorbed under normal conditions, which is why bloodstream entry (fungaemia) is a rare event specifically associated with critical illness, immunosuppression, or a breach such as a central venous catheter. (2) (3)

What Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079) is used for

Before taking Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079)

Do not take / not appropriate for

• Do not take Saccharomyces boulardii if you are critically ill or have a seriously weakened immune system (immunocompromised) -- rare but genuine, sometimes fatal, cases of the yeast entering the bloodstream (fungaemia) have occurred in these groups. (all countries) (2) (3)
• Do not take Saccharomyces boulardii if you have a central venous catheter (a central line) in place. (all countries) (2)
• Do not take it if you have a known allergy or hypersensitivity to it, or have had an allergic reaction to a previous dose. (all countries) (1)

Tell your clinician about

• Whether you are currently critically ill, hospitalised in intensive care, or have a weakened immune system for any reason (e.g. cancer treatment, organ transplant, HIV with low immune counts).
• Whether you have a central venous catheter or any other indwelling vascular line.
• Whether you are pregnant, breastfeeding, or considering giving this product to a young child.
• All other medicines and supplements you take, including any antifungal medicines.

How to take Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079)

• Follow the dose on your specific product's label, or the dose recommended by the clinician or pharmacist who suggested it, since labelled directions differ between the licensed-medicine version (France) and supplement-labelled versions (US, UK, and elsewhere).
• Capsules are usually swallowed whole with water; powder/sachet forms are usually mixed with a small amount of water, milk, or food just before taking, following the specific product's instructions.
• Because this product contains live yeast, avoid handling it with wet hands, and take particular care with hygiene if you are preparing it for someone in a hospital setting.
• Do not give this product to anyone who is critically ill, immunocompromised, or who has a central venous catheter.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7)

Missed dose

If you miss a dose, take the next one at its usual time. do not take an extra dose doses. If you are using this product as directed by a clinician for a specific condition, follow their guidance on missed doses.

Overdose

Significant overdose with this probiotic yeast product is not well documented in the sources reviewed for this dossier. If you experience persistent digestive symptoms, fever, or feel seriously unwell after taking a larger amount than directed, contact a pharmacist, clinician, or poison control service for guidance. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Antifungal medicines (such as itraconazole) can reduce the number of live Saccharomyces boulardii organisms and may reduce this product's effect; colonisation has been shown to decrease during and for about 2 weeks after itraconazole treatment. (7)
• As a live-organism product, it should not be combined with use in patients receiving treatment in a way that could introduce it into the bloodstream (e.g. via a central venous catheter) -- see serious warnings. (2)

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Confirm the person is not critically ill, immunocompromised, or fitted with a central venous catheter before use, especially in a hospital setting.

During treatment

• Watch for new fever, signs of infection, or feeling suddenly unwell, particularly in hospitalised or vulnerable patients.

Storage

Store at room temperature away from moisture and heat, as directed on the specific product's label, out of reach of children.

Frequently asked questions

References

1. SACCHAROMYCES BOULARDII 250 mg capsule -- dietary supplement labelU.S. Food and Drug Administration / DailyMed (NIH) -- dietary supplement label, Krewe Pharma · United States · accessed 2026-07-30 · source 1
2. Saccharomyces boulardii (Ultra-Levure) -- ajout d'une contre-indication chez les patients en état critique ou immunodéprimés (safety communication)Agence nationale de sécurité du médicament et des produits de santé (ANSM), France -- national medicines regulator · France (European Union) · accessed 2026-07-30 · source 2
3. Saccharomyces boulardii -- CMDh scientific conclusions and grounds for variation of product information (fungaemia risk review)European Medicines Agency (EMA) / Co-ordination Group for Mutual Recognition and Decentralised Procedures - Human (CMDh) -- EU-wide periodic safety update review, PSUSA/00009284/201702 · European Union · accessed 2026-07-30 · source 3
4. Saccharomyces boulardii -- Natural Health Product licensing (NPN) statusHealth Canada -- Natural and Non-prescription Health Products Directorate (Natural Health Products licensing, NPN) · Canada · accessed 2026-07-30 · source 4
5. Multiple Saccharomyces cerevisiae (Boulardii)-containing products -- ARTG listed (AUST L) complementary medicinesTherapeutic Goods Administration (TGA), Australia -- Australian Register of Therapeutic Goods (ARTG) · Australia · accessed 2026-07-30 · source 5
6. Saccharomyces boulardii -- consistently sold as an unlicensed food supplement in the UK; no MHRA/EMC-licensed medicinal product identifiedCross-referenced UK retailer listings (Nutri-Link, Supplement Hub, Optibac, Metagenics UK, Bio-Kult) plus NHS Specialist Pharmacy Service general food-supplement guidance · United Kingdom · accessed 2026-07-30 · source 6
7. Saccharomyces boulardii -- no dedicated Medsafe-approved medicine data sheet found; sold over-the-counter as a supplementSearch across Medsafe (New Zealand regulator) indexed pages and NZ retailer listings · New Zealand · accessed 2026-07-30 · source 7

Brand names by country

Single-ingredient Saccharomyces cerevisiae var. boulardii (strains CNCM I-745 / CNCM I-1079) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries