Overview

Saccharomyces boulardii (S. boulardii) is a probiotic yeast that is available over the counter as a supplement. It is often used for certain types of diarrhea. It may also be used for other reasons, but its benefits are not well defined. Common side effects include gas and upset stomach. In rare cases, it may cause an infection in some people who are at high risk for infections. Before taking S. boulardii, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is S. boulardii used for?

S. boulardii is a probiotic. It is commonly used for certain types of diarrhea. It is also used to improve gut health and boost the immune system, but its benefits for these uses are not well defined.

S. boulardii may also be used for other conditions as determined by your health care provider.

It is available as a dietary supplement in various strengths and dosage forms. Some dietary supplements that contain S. boulardii also contain many other ingredients, including other probiotics.

Note: The FDA has not reviewed S. boulardii products for safety and effectiveness. Learn more about dietary supplements here.

How does S. boulardii work (mechanism of action)?

S. boulardii is a species of yeast, which is a type of fungus. It is a probiotic, which means it is a live microbe that may provide health benefits in some people.

Your gut is home to millions of different microbes, which make up your gut microbiome. Unlike many other types of probiotics, S. boulardii is not usually found in your gut. It enters your gut when you take dietary supplements that contain S. boulardii or when you eat or drink fermented foods and beverages like kombucha, kefir, and certain types of yogurt.

S. boulardii can help improve the health of your microbiome by reducing the amount of bad bacteria and increasing the amount of good bacteria. When your gut microbiome is healthy, it can improve your ability to digest foods and resist infections. S. boulardii can also help reduce swelling (inflammation) in your gut. This may help reduce the risk of diarrhea in children who are taking antibiotics. It may also help your child’s gut recover more quickly from diarrhea that is caused by an infection. But it does not seem to help with diarrhea in adults.

Taking S. boulardii increases the levels of this yeast in your gut. But S. boulardii does not usually stay in your gut and become a part of your microbiome. Although it may improve the health of your microbiome for a short time, the long-term effects of S. boulardii are not well defined.

How should I store S. boulardii?

You should store S. boulardii according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight. Some S. boulardii products should be stored in the refrigerator, between 36 F and 46 F (2 C and 8 C), after they are opened. Follow the instructions on the label of the product you are using.

Side Effects

What are the most common side effects of S. boulardii?

The most common side effects of S. boulardii are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.

• Gas
• Upset stomach

There may be other side effects of S. boulardii that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of S. boulardii?

While less common, the most serious side effects of S. boulardii are described below, along with what to do if they happen.

Severe Allergic Reactions. S. boulardii may cause allergic reactions, which can be serious. Stop taking S. boulardii and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives, which can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Serious Infections. In very rare cases, some people who take probiotics, such as S. boulardii, can get a serious infection. This happens when S. boulardii moves into a part of the body where it is not supposed to be, such as your blood. This is most likely to happen in people who are very sick or have very weak immune systems, such as people with cancer or who are receiving chemotherapy. Call your health care provider right away if you have any of the following symptoms.

• Fever, sweats, chills, or muscle aches
• Tiredness
• Shortness of breath
• Fast heartbeat

Precautions

Who should not use S. boulardii?

Allergies to Ingredients. People who are allergic to any of the following should not take S. boulardii.

• Florastart
• Florastor
• Rezyst
• S. boulardii
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific S. boulardii products they stock.

What should I know about S. boulardii before using it?

If S. boulardii was prescribed to you by a health care provider, take it as prescribed. If you are taking S. boulardii as an over-the-counter supplement, follow the instructions that come with the product or take it as your health care provider recommends. If you have any questions about how to take S. boulardii, talk to your health care provider.

Do not share S. boulardii that was prescribed for you by a health care provider with other people, even if they have the same condition as you. It may harm them.

Keep S. boulardii out of the reach of children. Since some S. boulardii products should be kept in a refrigerator, take special precautions to keep them away from children who also use the refrigerator.

If you or your child has trouble swallowing S. boulardii capsules, ask your pharmacist if it is safe to open the capsules and sprinkle the contents on food instead.

Premature infants can be at greater risk of side effects from probiotics, such as S. boulardii. Talk to your health care provider about the risks if your infant was born prematurely.

S. boulardii is a species of yeast. Within that species are many different strains. Each strain of S. boulardii may have slightly different effects in the body. This means that some strains of S. boulardii may have certain effects that other strains do not have. If the product you are using contains a specific strain, it should be listed on the product label as the string of numbers or letters that come after “S. boulardii.” If you switch to a different strain of S. boulardii, it may not have the same effects or side effects. Talk to your health care provider if you have questions or concerns.

Some probiotic products have been found to contain other microbes that are not listed on the label, and that may cause serious health problems. The FDA has not tested S. boulardii products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using S. boulardii?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if S. boulardii is right for you.

In particular, make sure that you discuss any of the following.

Central Line or Port.A central venous catheter (central line) or port is a small tube placed into a vein that can be used to give medicines and fluids directly into the vein (intravenously, or IV). These tubes become infected by microbes, including probiotics. If you have a central line or port, speak with your health care provider before taking S. boulardii.

Yeast Allergy.S. boulardii is a type of yeast. If you have a yeast allergy, speak with your health care provider before taking S. boulardii.

Other Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• An autoimmune condition
• Cancer
• Immune problems, such as a weak immune system

Other Medicines and Supplements.S. boulardii may interact with other medicines and supplements. Before taking S. boulardii, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how S. boulardii could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if S. boulardii passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does S. boulardii interact with foods or drinks?

There are no known interactions between S. boulardii and foods or drinks.

It is unknown if drinking alcohol will affect S. boulardii.

Does S. boulardii interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking S. boulardii.

• A medicine that suppresses the immune system
• An antifungal medicine, which is used to treat certain fungal infections
• Chemotherapy, which is used to treat certain cancers

The interactions between S. boulardii and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with S. boulardii is incomplete. Always check with your health care provider before taking S. boulardii with any medicines.

Dosing

What should I do if I accidentally use too much S. boulardii?

If you or someone else has used too much S. boulardii, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

S. boulardii products may contain many different ingredients, including other probiotics. Read the product label closely and speak with a health care provider about how to take S. boulardii safely. Do not take double or extra doses, even if you miss a dose.