Overview

Limosilactobacillus fermentum (L. fermentum) is a probiotic bacteria that is available over the counter as a supplement and in some fermented vegetables and dairy products. It is commonly used to improve the health of the gut, vagina, and immune system, but its benefits are not well defined. Common side effects include gas and an upset stomach. Serious side effects are rare but include infections in some people who are at high risk for infections. Before using L. fermentum, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is Limosilactobacillus fermentum (L. fermentum) used for?

L. fermentum is a probiotic that is commonly used to improve the health of the gut, vagina, and immune system, but its benefits are not well defined.

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

Note: The FDA has not reviewed L. fermentum for safety and effectiveness. Learn more about dietary supplements here.

How does L. fermentum work (mechanism of action)?

L. fermentum is a species of bacteria. It is a type of probiotic, which means it is a live microbe that may provide health benefits in some people.

Your body is home to millions of different microbes, which make up part of your microbiome. L. fermentum is naturally found in your gut. You can also get L. fermentum from dietary supplements and some fermented foods, including certain vegetables, dairy products, and breads.

L. fermentum makes a substance called lactic acid. Lactic acid can help improve the health of your microbiome by reducing the amount of bad bacteria and increasing the amount of good bacteria. When the microbiome in your gut and mouth are healthy, it can make you more able to digest foods and resist various types of infections, including dental cavities. When the microbiome in your vagina is healthy, it can make you more able to resist vaginal infections.

Taking L. fermentum by mouth increases the levels of this bacteria in your gut. This may help improve the health of your microbiome. But there are many factors that can affect whether a probiotic survives in your body. When you take L. fermentum by mouth, it may not always survive long enough to grow and multiply in your gut or vagina. As a result, its benefits are not well defined and may be different for each person. It is not clear whether L. fermentum can help with any health problems.

How should I store L. fermentum?

You should store L. fermentum 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.

Side Effects

What are the most common side effects of L. fermentum?

The most common side effects of L. fermentum 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 L. fermentum 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 L. fermentum?

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

Severe Allergic Reactions. L. fermentum may cause allergic reactions, which can be serious. Stop using L. fermentum 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 that 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 use probiotics, such as L. fermentum, can get a serious infection. This happens when L. fermentum 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 who 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 L. fermentum?

Allergies to Ingredients. People who are allergic to any of the following should not use L. fermentum.

• L. fermentum
• Lactobacillus fermentum
• Limosilactobacillus fermentum
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific L. fermentum products they stock.

What should I know about L. fermentum before using it?

L. fermentum is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are using, or use it as recommended by your health care provider.

Keep L. fermentum out of the reach of children.

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

The full name of L. fermentum, Limosilactobacillus fermentum, has only been around since 2020. Before then, this species of bacteria was called Lactobacillus fermentum. You may still see both of these names on product labels. These are the same species of bacteria.

Probiotics, such as L. fermentum, are usually measured in colony forming units (CFUs). Each CFU is equal to one living bacteria. The number of CFUs listed on the product label tells you how many living bacteria should be in that product on the day that it expires. Since bacteria slowly die off over time, the number of living bacteria in the product may be higher than the amount on the label.

Many probiotic products contain multiple species of microbes. Different microbes can have different effects in the body. It is important to read the product label closely to understand which species of bacteria are in that product.

L. fermentum is a species of bacteria. Within that species are many different strains. Each strain of L. fermentum may have slightly different effects in the body. This means that some strains of L. fermentum 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 “L. fermentum.” If you switch to a different strain of L. fermentum, 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 may cause serious health problems. The FDA has not tested L. fermentum 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 L. fermentum?

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 L. fermentum 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 can become infected by microbes, including probiotics. If you have a central line or port, speak with your health care provider before using L. fermentum.

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.L. fermentum may interact with other medicines and supplements. Before using L. fermentum, tell your health care provider about any prescription or 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 L. fermentum 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 L. fermentum passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does L. fermentum interact with foods or drinks?

There are no known interactions between L. fermentum and foods or drinks.

It is unknown if drinking alcohol will affect L. fermentum.

Does L. fermentum 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 using L. fermentum.

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

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

Dosing

What should I do if I accidentally use too much L. fermentum?

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

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