What is Lactobacillus reuteri?

Lactobacillus reuteri is a lactic acid-producing probiotic bacterium that naturally colonizes the human digestive tract, oral cavity, and urogenital system. Unlike many other probiotics, L. reuteri is considered an indigenous human commensal — meaning it evolved alongside us — making it exceptionally well-suited to survive and thrive in the human body. It is one of the most clinically studied probiotic species in the world, with hundreds of human trials across infants, children, and adults.

How does Lactobacillus reuteri work?

L. reuteri works through several pathways at once. It produces reuterin, a natural broad-spectrum antimicrobial that keeps harmful bacteria in check without disrupting the broader microbiome. It also strengthens the gut lining, reducing leakiness, and communicates with immune cells to calm inflammation and train the immune system toward better balance. Certain strains also interact with the nervous system through the gut-brain axis, which may explain its calming effects on colic and mood.

What forms does Lactobacillus reuteri come in?

Infant oral drops (DSM 17938) are the most established form for colic. Chewable tablets and lozenges are popular for oral and dental health. Capsules are used for adult digestive and immune benefits. Vaginal formulations use specific strains (RC-14) shown to restore healthy vaginal flora. Always match the strain to the intended use — not all L. reuteri products are interchangeable.

Where it comes from:

L. reuteri was first isolated in 1962 by German microbiologist Gerhard Reuter, who found it naturally present in human and animal intestines. It was formally named after him in 1980. The discovery that it produces the potent antimicrobial compound reuterin sparked decades of research. Swedish company BioGaia commercialized the first human-use strains in the 1990s and has funded or collaborated on much of the clinical research. It was reclassified in 2020 from the Lactobacillus genus to Limosilactobacillus, though L. reuteri remains the widely used common name.

What does Lactobacillus reuteri help with?

• Infant colic and crying: L. reuteri DSM 17938 is the most evidence-backed natural remedy for infant colic — the condition where otherwise healthy babies cry for hours for no clear reason. Studies show it can significantly reduce daily crying time within two to three weeks, and it works best in breastfed infants. Researchers believe it calms gut spasms and reduces gas through its effect on the infant's developing microbiome.
• Gut health and digestion: L. reuteri helps balance the gut microbiome by crowding out harmful bacteria and producing compounds that reduce gut inflammation. It strengthens the intestinal lining, which can ease bloating, cramping, and irregular bowel movements. People with irritable bowel symptoms often report feeling more comfortable within a couple of weeks.
• H. pylori infection: H. pylori is the bacteria behind most stomach ulcers, and standard antibiotic treatment doesn't always work well on its own. Taking L. reuteri alongside antibiotic therapy has been shown to improve eradication rates and reduce the side effects of the antibiotics — making the treatment both more effective and easier to tolerate.
• High cholesterol: Certain strains of L. reuteri — particularly DSM 17938 and NCIMB 30242 — have shown meaningful reductions in LDL (bad) cholesterol in clinical trials. The bacteria appear to interfere with how the gut recycles bile acids, which prompts the liver to pull more cholesterol from the blood to make new ones. Effects typically become noticeable after four to eight weeks of consistent use.
• Immune health and recurring infections: L. reuteri helps train immune cells to respond more appropriately — calming overreactions and boosting defenses against genuine threats. In daycare-aged children, supplementation has been linked to fewer sick days and respiratory infections. Adults taking it regularly may also see reduced frequency of common colds and gut infections.
• Vaginal health and bacterial vaginosis: Specific strains — particularly RC-14 combined with rhamnosus GR-1 — have strong clinical support for restoring and maintaining healthy vaginal flora. They colonize the vaginal lining and help restore the protective acidic environment that keeps yeast and harmful bacteria from taking hold. They are used both to treat bacterial vaginosis and to prevent recurrence.
• Oral health and gum disease: L. reuteri lozenges (DSM 17938 and ATCC PTA 5289) have shown real benefits for people with gum disease, reducing inflammation markers, bleeding, and plaque compared to placebo. The bacteria appear to compete with harmful oral bacteria and produce antimicrobial compounds right where they're needed in the mouth.
• Bone density (osteoporosis risk): Emerging research — including human trials — suggests that L. reuteri ATCC PTA 6475 may slow bone loss in older women by reducing gut inflammation and influencing how the body absorbs calcium and signals bone-building cells. This is a newer area of research, but the early results from controlled trials are encouraging.
• Eczema and skin inflammation: The gut-skin connection means that improving microbiome balance can sometimes ease inflammatory skin conditions. Trials in infants and children have shown that L. reuteri supplementation during pregnancy or early infancy may reduce the risk or severity of eczema, likely by helping the immune system develop a more balanced response to allergens.
• Constipation and bowel regularity: L. reuteri has been shown in multiple trials in children to increase bowel movement frequency and soften stool consistency. It appears to speed up gut transit time by interacting with nerves in the gut wall. Adults with functional constipation may also benefit, though the pediatric evidence is stronger.

What can Lactobacillus reuteri help prevent?

• Recurrence of bacterial vaginosis: RC-14/GR-1 combination has clinical evidence for preventing relapse after treatment
• Antibiotic-associated diarrhea: taking L. reuteri alongside antibiotics reduces the risk of disruption-related diarrhea
• Recurring H. pylori after eradication: adjunct use may reduce reinfection rates
• Eczema onset in high-risk infants: prenatal and early postnatal supplementation shows preventive potential in atopy-prone families

Which foods are rich in Lactobacillus reuteri?

1. Sourdough bread (traditional): Traditional long-fermented sourdough can harbor L. reuteri naturally, as it is a native inhabitant of fermented grain environments — though amounts vary widely by starter culture.
2. Human breast milk: L. reuteri is one of the most consistently found probiotic species in human breast milk, which is how infants naturally receive this beneficial bacterium — reinforcing its status as a true human commensal.
3. Fermented dairy (raw milk cheeses, kefir): L. reuteri is found naturally in the gut of ruminants and can be present in unpasteurized dairy and artisanal cheeses, though commercial pasteurized products rarely contain live strains.
4. Fermented meat products (certain salami, sausages): Traditional dry-fermented meats can contain L. reuteri as part of their natural fermentation microbiome, particularly in artisanal European-style products — though concentrations are low.
5. Fermented vegetables (traditional, not vinegar-pickled): Naturally fermented vegetables like traditional kimchi or brine-cured pickles may contain small amounts of L. reuteri alongside other lactobacillus species, contributing to a broader probiotic ecosystem.

Practical Tips:

While L. reuteri exists in certain fermented foods, the concentrations are typically far too low and inconsistent to match therapeutic supplement doses. For specific health goals — especially infant colic, cholesterol, or vaginal health — a clinically studied supplement strain is the reliable approach. Supporting foods that promote a healthy microbiome environment include high-fiber vegetables, legumes, oats, and other fermented foods like yogurt and kefir, which feed and sustain beneficial bacteria including L. reuteri.

What are the side effects of Lactobacillus reuteri?

• Mild bloating or gas in the first few days: usually resolves as the gut adjusts
• Loose stools or slight change in bowel habits when first starting
• Rare: mild abdominal discomfort that settles within a week
• Very rare: theoretical risk of probiotic bacteremia in severely immunocompromised individuals — avoid use in this population without medical supervision
• Infant drops are considered very safe; some infants may spit them up or show temporary feeding changes

Good to know:

L. reuteri has an excellent safety record across hundreds of clinical trials, including in premature infants and pregnant women. The vast majority of people experience no side effects at all.

How much Lactobacillus reuteri should you take?

• Recommended daily: Adults: 1–10 billion CFU daily (most clinical trials use 100 million to 1 billion CFU for L. reuteri specifically — higher is not always better; match dose and strain to your goal). Infants (colic): 100 million CFU (5 drops of BioGaia Protectis) daily.
• Best time of day: Anytime, but consistency matters more than timing. Many people prefer taking it with breakfast or before bed. For oral health lozenges, use after brushing teeth at night.
• With or without food: Best taken with or just after a meal — food buffers stomach acid and improves survival of the bacteria through the digestive tract. Avoid taking with very hot drinks.
• Time to effect: Infant colic: 1–3 weeks. Digestion and gut comfort: 1–2 weeks. Cholesterol: 4–8 weeks. Vaginal health: 4–8 weeks. Oral health: 4–12 weeks.
• How long to take it: For ongoing gut and immune health, continuous daily use is appropriate and well-supported by safety data. For specific conditions like H. pylori adjunct therapy or BV prevention, 4–12 week courses are typical. Cycling is not required but some people use it seasonally or during high-stress periods.