Lactobacillus Reuteri: Which Strains Were Studied and What They Showed

Quick answer. Lactobacillus reuteri, now officially named Limosilactobacillus reuteri, is a lactic acid bacterium found in the human gut and breast milk. Its human research is really research on a few coded strains. The most studied, DSM 17938, has reduced crying in breastfed infants with colic in several trials, but a larger community-based trial found no benefit, and its results for abdominal pain and constipation in children are mixed. Other strains were tested for bone loss (one positive trial in women aged 75 to 80, then a larger null one in women in their 50s), vaginal health (with an L. rhamnosus strain) and gum disease, with mixed results. Side effects in trials were usually similar to placebo, but rare infections have occurred in very sick patients, including one fatal case in an extremely preterm newborn.

What Lactobacillus reuteri is

L. reuteri is a species of bacteria. Different strains live in the gut of people and of animals such as pigs, mice and rats, and the species has been found in human breast milk. In 2020, taxonomists split the old Lactobacillus genus into 25 genera based on whole-genome data. L. reuteri moved to the new genus Limosilactobacillus, and PubMed's subject headings now list it as Limosilactobacillus reuteri. We use the familiar name below.

Strain matters more than species. A probiotic is a live microorganism that gives a health benefit when taken in adequate amounts, and the NIH Office of Dietary Supplements (ODS) notes that effects can differ from strain to strain. The trials below used these coded strains:

• DSM 17938, given as oil drops in infant trials. It was derived from an older strain, ATCC 55730, by removing two plasmids that carried genes for tetracycline and lincosamide resistance. The new strain lost those resistances.
• ATCC PTA 6475, tested for bone loss and, with DSM 17938, in H. pylori treatment.
• RC-14, almost always given with L. rhamnosus GR-1 for vaginal health. Early papers called it L. fermentum RC-14.
• ATCC PTA 5289, given with DSM 17938 in lozenges for gum health.

A study of one coded strain does not tell you what an unnamed strain of the same species will do.

What human studies have tested

Studies are grouped by strain. Doses are as the papers report them.

What the findings suggest

Infant colic (DSM 17938). Pooled raw data from four double-blind trials showed a strong effect in breastfed infants and no significant effect in formula-fed infants. A larger trial in Melbourne, which used a validated crying diary, found no benefit and more fussing with the probiotic. It recruited mostly from an emergency department, and crying fell steadily in both groups. Strength: moderate for breastfed infants with colic, and limited or conflicting for formula-fed infants.

Preventing colic and reflux-type spitting up. In one large Italian trial, newborns given DSM 17938 for 90 days cried less and spit up less at 3 months. The Cochrane review of prevention trials found no clear reduction in new colic cases, with low certainty. Strength: limited.

Children's abdominal pain. Single trials disagree. Weizman found less pain; Maragkoudaki found that pain fell just as much with placebo. The newest meta-analysis of seven DSM 17938 trials found no consistent effect, with very low certainty. A 2023 Cochrane review of all probiotics for children's functional abdominal pain found low-certainty evidence of more treatment success but could not analyze by strain. Strength: low.

Children's constipation. DSM 17938 added nothing to the laxatives macrogol or lactulose in two trials, and a 2022 Cochrane review of all probiotics found insufficient evidence of benefit. Strength: low, mostly null.

Bone (ATCC PTA 6475). One 12-month trial in women aged 75 to 80 with low bone density found about half as much bone loss at the shin. A larger 2-year trial in women in their 50s, at two doses (1 billion and 10 billion CFU a day), found no effect. Its authors say the strain "should not be recommended" to women of that age to prevent bone loss. Neither trial was designed to test fractures. Strength: very limited.

Vaginal outcomes (RC-14 with GR-1). Two small trials from the 2000s reported higher BV cure rates when the pair was added to antibiotics. A 2021 trial in Chinese women found no added benefit, and a UK pregnancy trial found no change in the vaginal microbiota and no RC-14 in the vagina. These results belong to the two-strain pair taken by mouth. GR-1 is an L. rhamnosus strain, covered in our L. rhamnosus review, and our review of L. crispatus explains how vaginal and oral products differ. Strength: low and inconsistent.

Gums (DSM 17938 with ATCC PTA 5289). Lozenges after professional deep cleaning produced modest extra gains in deeper pockets in small trials. For people with gingivitis, a meta-analysis found no significant L. reuteri effect on gingival or plaque index. In 2020 the European Food Safety Authority (EFSA) found the evidence for these lozenges insufficient for a "normal gum function" claim: of the two trials in people with gingivitis but no periodontitis it could draw conclusions from, one showed a large effect and one showed none. Strength: low.

H. pylori. A 2019 meta-analysis of Lactobacillus add-ons to triple therapy found higher eradication in the L. reuteri subgroup (RR 1.18; 95% CI 1.03 to 1.34). A placebo-controlled trial with bismuth quadruple therapy found no difference in eradication, only less abdominal pain. Strength: limited.

What guidelines say. The 2023 World Gastroenterology Organisation (WGO) guideline lists DSM 17938, at its highest evidence level, for managing and preventing colic, children's functional abdominal pain, acute diarrhea in children and preventing necrotizing enterocolitis (NEC) in preterm infants. The American Gastroenterological Association's (AGA) 2020 technical review rated as high certainty the evidence that DSM 17938 or its parent strain ATCC 55730 lowered severe NEC in preterm, low-birth-weight infants. The AGA also concluded that probiotics do not appear to benefit children in North America with acute gastroenteritis, so the two bodies differ on childhood diarrhea. The 2023 position paper of the European pediatric society ESPGHAN made strain-specific recommendations, only where at least two trials of a similar strain existed, for conditions including infant colic and children's functional abdominal pain; its abstract, the part we could read, does not name the strains.

Where the evidence is limited or conflicting

• One company, many trials. The best-known strains (DSM 17938, ATCC PTA 6475, ATCC PTA 5289) come from one manufacturer. It part-funded the first bone trial, supplied the product and ran the randomization in the second, made the gum lozenges and applied for the EFSA gum claim. The UK pregnancy trial was charity-funded.
• Small and short. Most trials in the table enrolled fewer than 150 people and lasted 12 weeks or less.
• Colonization is inconsistent. DSM 17938 was found in the stool of 45% of treated infants in Melbourne. RC-14 was not found in the vagina in the UK trial, and the GR-1/RC-14 strains were rarely detected in the Chinese trial.
• Combinations. RC-14 was almost always tested with GR-1, and the gum and H. pylori products paired two L. reuteri strains, so single-strain effects cannot be separated.
• A striking follow-up needs care. A 10-year follow-up of the Italian newborn trial reported functional abdominal pain in 13% of children who had been given DSM 17938 vs 80% given placebo. Fewer than half of the original children were assessed, and the authors call it an association, not proof.
• Unpublished trials. ClinicalTrials.gov lists two manufacturer-sponsored colic trials completed in 2025 and 2026; we found no published results on November 8, 2026.

Safety

In trials. Side effects were generally similar with L. reuteri and placebo. In the first bone trial, adverse events occurred in 80% of women on the probiotic and 87% on placebo, and in the 2-year trial no serious adverse event was judged treatment-related. Cochrane reviews of children's trials found no excess of serious adverse events, with low or very low certainty. NIH ODS describes probiotic side effects as usually minor, such as gas.

Infections. Lactobacilli rarely cause infections such as bacteremia or endocarditis, mostly in people with diabetes or weakened immunity and risk factors such as prosthetic heart valves, according to a review of 48 case reports published from 2019 to 2021. A 2019 case report describes fatal L. reuteri sepsis in an extremely preterm newborn who received the probiotic under a hospital protocol and had a central venous catheter. In 2023, the FDA warned that probiotics given to preterm infants can cause invasive, potentially fatal disease, and said it has not approved any probiotic product as a drug or biological product for infants.

Antibiotic resistance genes. DSM 17938 exists because its parent strain carried potentially transferable resistance genes, a reminder that strain identity matters for safety too.

Pregnancy. In the UK trial of GR-1 and RC-14 taken from early pregnancy, no serious adverse events were linked to the capsules. There were 3 miscarriages in the probiotic group and 1 with placebo, a difference the trial was not designed to test. A 12-week placebo-controlled trial in 86 pregnant women reported no adverse issues. Ask your obstetric clinician before use in pregnancy or breastfeeding.

Medicines and limits. We found no documented drug interactions specific to L. reuteri. If you take antibiotics or immune-suppressing medicines, or have a central line, ask your doctor or pharmacist first. We found no official upper intake level for probiotics. Follow your product label.

What research does not establish

• That L. reuteri, as a species, has any proven benefit; results belong to coded strains.
• That DSM 17938 helps formula-fed infants with colic, or that any strain treats colic, abdominal pain, constipation, BV, gum disease or H. pylori on its own.
• That ATCC PTA 6475 prevents bone loss or fractures in most women.
• That oral RC-14 reliably reaches the vagina.
• That L. reuteri supports hair growth or skin aging; our search found no clinical trial of either.

How we reviewed the evidence

On November 8, 2026, we ran nine targeted PubMed searches by strain and outcome and screened the 132 records they returned by title and abstract, with overlap. Extra searches covered hair and skin trials, retractions and taxonomy. We read full texts where available and abstracts otherwise, plus the WGO 2023 guideline, the AGA technical review and AGA's 2020 news release, the NIH ODS fact sheet, the FDA's 2023 letter, EFSA's 2020 opinion and ClinicalTrials.gov (272 L. reuteri intervention records). We could not access the full AGA guideline or ESPGHAN paper; we report ESPGHAN from its abstract only. We excluded animal and lab-only studies, heat-killed bacteria and unnamed strains. None of the cited studies is listed as retracted in PubMed. Vinatura did not run any trials of L. reuteri.

Vinatura Research Perspective

We asked four questions of each study: which coded strain, in what form and amount, in whom, and whether the outcome was a symptom, a lab measure or a hard endpoint such as fractures. DSM 17938 was studied mainly in infants and children at about 100 to 200 million CFU a day. ATCC PTA 6475 was studied in women's bones at 1 to 10 billion. RC-14 was studied with GR-1 for vaginal health at 1 to 2.5 billion CFU of each strain per dose. A species-level "benefits" list merges these into claims that no single trial tested.

Two observations stood out. First, more CFU did not mean more effect: in the 2-year bone trial, 10 billion CFU a day did no better than 1 billion and neither beat placebo, while the colic signal came at 100 million CFU a day. Second, the strongest results often came from small early trials; later trials, often larger or in different populations, were more often null: colic in Melbourne, bone in early menopause, BV in China.

Our assessment: moderate evidence that DSM 17938 reduces crying in breastfed infants with colic; low or very low evidence for children's abdominal pain, gum health and H. pylori support; mostly null evidence for children's constipation and early postmenopausal bone loss; and low, inconsistent evidence for oral RC-14 with GR-1 in vaginal health. Large independent trials in formula-fed infants, a fracture-outcome trial in older women with low bone density, published results of the completed colic trials, and studies that track strain colonization would change this assessment.

Where this ingredient appears in Vinatura products

L. Salivarius Oral Probiotic lists Lactobacillus reuteri 1 billion CFU per serving (1 chewable mint tablet), with L. salivarius, L. acidophilus and L. plantarum. Women's Probiotic lists Lactobacillus reuteri Complex 25 mg (1.25 billion CFU) per delayed-release capsule, with five other Lactobacillus complexes. Neither page names strains. The studies above did not test these products.

Frequently asked questions

What are the benefits of Lactobacillus reuteri? Benefits were tested for specific strains, not the species. The most consistent finding is less crying in breastfed infants with colic given DSM 17938. Most other uses have small, mixed or null trials.

What are the side effects of L. reuteri? In trials, side effects were usually mild and similar to placebo. Rare, serious infections have occurred in very sick or preterm patients, and the FDA has warned that probiotics can cause serious infections in preterm infants.

Does L. reuteri help with bone loss? One trial in women aged 75 to 80 with low bone density found less shin bone loss with ATCC PTA 6475. A larger 2-year trial in women in their 50s found no effect, and neither trial was designed to test fractures.

How much did studies use? Trials used about 100 million CFU a day for infants and up to 10 billion CFU a day in the bone trials. These are study amounts, not recommendations. Follow your product label and ask a healthcare professional.

References

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Editorial note: This article reviews published research for educational purposes. It does not establish the effects or safety of any specific supplement, including Vinatura products, and is not medical advice. Written by Vinatura Editorial Team. Last reviewed November 2026.