The human body contains 10–100 trillion bacteria (1).

Most of these bacteria live inside your gut and are collectively known as microbiota. They play an important role in maintaining optimal health.

While there are many benefits to having a healthy balance of gut bacteria, an imbalance is linked to numerous diseases (2, 3).

One of the most well-studied friendly bacteria is Lactobacillus rhamnosus (L. rhamnosus), which is available as a dietary supplement and added to a variety of foods, such as dairy products.

This article reviews the benefits, side effects, and dosage of L. rhamnosus.

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L. rhamnosus is a type of bacteria found in your intestines.

It belongs to the genus Lactobacillus, a type of bacteria that produce the enzyme lactase. This enzyme breaks down the sugar lactose — which is found in dairy — into lactic acid.

Bacteria from this genus, such as L. rhamnosus, are considered probiotic.

Probiotics are live microorganisms that can offer health benefits when consumed (4).

Hundreds of studies support the benefits of L. rhamnosus.

Uniquely adapted to survive in acidic and basic conditions within your body, this bacterium can also adhere to and colonize your intestinal walls. Such characteristics give L. rhamnosus a better chance of survival — so it may offer longer-term benefits (5, 6).

There are many different strains, each with different characteristics (7).

L. rhamnosus is available as a probiotic supplement and often added to yogurts, cheeses, milk, and other dairy products to boost probiotic content.

It can also be added to dairy for other reasons. For example, L.rhamnosus plays a key role in cheese ripening, which enhances flavor (8, 9).

However, many products that contain L. rhamnosus don’t typically include it in the ingredients list.

Summary L. rhamnosus is a member of the probiotic Lactobacillus genus of bacteria. It is adapted to survive in your gut, thus potentially offering longer-term benefits.

L. rhamnosus has numerous potential benefits and uses for your digestive system, as well as other areas of health.

1. May Prevent and Treat Diarrhea

Diarrhea is a common issue sometimes caused by bacterial infection.

In most situations, diarrhea is relatively harmless. However, persistent diarrhea can cause fluid loss, which may lead to dehydration.

Studies show that L. rhamnosus may help prevent or treat various types of diarrhea.

For example, L. rhamnosus may protect against antibiotic-related diarrhea. Antibiotics can disrupt microbiota, which may result in digestive symptoms like diarrhea (10, 11).

For instance, a review of 12 studies in 1,499 people found that supplementing with a specific strain called L. rhamnosus GG reduced the risk of antibiotic-related diarrhea from 22.4% to 12.3% (12).

In addition, taking a probiotic during and after antibiotic use can help restore your healthy gut bacteria, since antibiotics often kill them alongside harmful bacteria.

What’s more, L. rhamnosus may protect against various other types of diarrhea, such as traveler's diarrhea, acute watery diarrhea, and acute gastroenteritis-related diarrhea (13, 14, 15).

2. May Relieve IBS Symptoms

Irritable bowel syndrome (IBS) affects 9–23% of adults worldwide (16).

While its cause is unknown, IBS causes uncomfortable symptoms, such as bloating, abdominal pain, and unusual bowel movements (16).

Interestingly, there may be a link between IBS and changes in the body’s natural gut flora.

For instance, people with IBS may have fewer Lactobacillus and Bifidobacterium bacteria but more potentially harmful Clostridium, Streptococcus, and E. coli (17, 18).

Human studies note that Lactobacillus-rich foods or supplements may relieve common IBS symptoms, such as abdominal pain (19, 20, 21).

Additionally, animal studies have found that L. rhamnosus strains may strengthen gut barriers, which may help relieve IBS symptoms (22).

However, more research in humans is needed before recommendations can be made.

3. Aids Gut Health

Like other probiotic bacteria, L. rhamnosus is great for your digestive health.

It belongs to the Lactobacillus family, which produces lactic acid. Lactic acid helps prevent the survival of potentially harmful bacteria in your digestive tract.

For instance, L. rhamnosus can prevent Candida albicans, a type of harmful bacteria, from colonizing your intestinal walls (23).

L. rhamnosus not only prevents bad bacteria from colonizing but also encourages the growth of beneficial bacteria, such as Bacteroides, Clostridia, and bifidobacteria (24).

What’s more, L. rhamnosus helps increase the production of short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate (25).

SCFAs are made when your healthy gut bacteria ferment fiber inside your digestive tract. They are a source of nourishment for the cells lining your colon (26).

In addition, studies link SCFAs to various benefits, including protection against colon cancer, weight loss, and lower blood sugar levels (27, 28, 29).

4. May Protect Against Cavities

Dental cavities are a common occurrence, especially in children (30).

They’re formed by harmful bacteria in your mouth. These bacteria produce acids that break down your enamel, or the outer layer of your teeth (31).

Probiotic bacteria like L. rhamnosus have antimicrobial properties, which may help fight these harmful bacteria (32).

In one study, 594 children received either regular milk or milk containing L. rhamnosus GG for 5 days per week. After 7 months, children in the probiotic group had fewer cavities and a lower number of potentially harmful bacteria than children in the regular-milk group (33).

Another study in 108 adolescents found that taking a lozenge containing probiotic bacteria — including L. rhamnosus GG — significantly reduced bacterial growth and gum inflammation, compared to a placebo (34).

That said, more human studies are needed before recommendations can be made.

5. May Help Prevent UTIs

A urinary tract infection (UTI) is an infection that can happen anywhere along your urinary tract, including your kidneys, bladder, and urethra.

It is much more common in women and typically caused by two strains of bacteria — Escherichia coli (E. coli)and Staphylococcus saprophyticus (35, 36).

Some studies indicate that probiotic bacteria, including certain strains of L. rhamnosus, may prevent UTIs by killing harmful bacteria and restoring vaginal flora.

For instance, an analysis of 5 studies in 294 women found that several Lactobacillus bacteria, including L. rhamnosus, were safe and effective at preventing UTIs (37).

Other studies discovered that the L. rhamnosus GR1 strain — given either orally or intravaginally — was particularly effective at killing harmful bacteria in the urinary tract (38, 39).

However, not all L. rhamnosus strains may help treat UTIs. For example, L. rhamnosus GG strains don’t attach well to vaginal walls and may not be effective (40).

While these findings are promising, more human research is needed.

6–10. Other Potential Benefits

L. rhamnosus has been linked to several other potential health benefits. However, these properties are backed by fewer or weaker studies:

  1. May promote weight loss. L. rhamnosus may suppress appetite and food cravings, especially in women (41, 42).
  2. May increase insulin sensitivity. Animal studies show that several L. rhamnosus strains may improve insulin sensitivity and blood sugar control (43, 44, 45, 46).
  3. May reduce blood cholesterol. One mouse study found that L. rhamnosus lowered blood cholesterol levels and had a similar effect on cholesterol metabolism as statins, a class of drugs that helps treat high cholesterol (47).
  4. May fight allergies. L. rhamnosus strains may help prevent or relieve allergy symptoms by promoting the growth of friendly gut bacteria and suppressing the growth of harmful bacteria (48, 49, 50).
  5. May help treat acne. In a small study in 20 adults, taking an L. rhamnosus SP1 supplement helped reduce the appearance of acne (51).
Summary L. rhamnosus may boost your overall digestive health, potentially treating diarrhea, relieving IBS symptoms, and strengthening your gut. It may also protect against cavities and UTIs. A number of other potential benefits haven’t been rigorously tested.

L. rhamnosus probiotic supplements can be purchased in health food stores or online.

They can contain only L. rhamnosus species or these species combined with other probiotic bacteria.

Probiotic bacteria are measured by the number of living organisms per capsule, known as colony-forming units (CFU). A typical L. rhamnosus supplement holds approximately 10 billion live bacteria — or 10 billion CFU — per capsule.

For general health, 1 capsule containing at least 10 billion live bacteria is sufficient.

To help prevent antibiotic-related diarrhea, take 2 capsules of L. rhamnosus GG daily providing 10 billion live bacteria or 1 capsule with over 20 billion live bacteria (52).

Take the probiotic supplement a few hours after your antibiotic(s), then continue for at least one week after your course of antibiotics to help restore a healthy gut.

Dosage guidelines have not been established for other uses of L. rhamnosus, but experts suggest that a similar daily dose may be appropriate.

Keep in mind that L. rhamnosus is sometimes added to dairy products — such as yogurts and milk — to boost their probiotic content and to cheeses to aid the ripening process.

Summary L. rhamnosus can be taken as a probiotic supplement and is often added to various foods, especially dairy products. This means that your diet may naturally provide an extra dose of this bacterium.

L. rhamnosus products are generally safe and well tolerated with few side effects.

In some cases, people may experience symptoms like stomach bloating or gas (53).

That said, people with compromised immune systems — such as those with HIV, AIDS, or cancer — should avoid L. rhamnosus and other probiotics (or dairy products with added probiotics), as such supplements may cause an infection.

Likewise, if you’re taking drugs that may weaken your immune system — such as steroid drugs, cancer drugs, or medication for an organ transplant — you should avoid taking probiotics.

If you fall into these criteria or are concerned about side effects, consult with your medical provider before taking a probiotic supplement or dairy products with added probiotics.

Summary L. rhamnosus is generally safe with few side effects. However, those with compromised immune systems or taking certain medications should avoid taking probiotics or first consult with a medical professional.

L. rhamnosus is a type of friendly bacteria naturally found in your gut.

Its health benefits include relieving IBS symptoms, treating diarrhea, strengthening your gut health, and protecting against cavities.

L. rhamnosus is available as a probiotic supplement and found in some dairy products.

If you are interested in improving your digestive health, consider trying out L. rhamnosus.