What Is Lactobacillus Rhamnosus Good For? What the Trials Measured

Lactobacillus rhamnosus has more trials than any other lactobacillus, and they belong to particular strains, not the species. One strain roughly halved antibiotic-associated diarrhoea in children (relative risk 0.48 across five trials); given to mothers in late pregnancy and then to the baby, it reduced eczema by age four in one trial (relative risk 0.57), while given to babies alone it did not (hazard ratio 0.95); and in 971 children with a stomach bug it made no difference to the illness. A label that names the species but not the strain cannot carry those results. This page is one spoke of the Wellgard probiotics guide.

Evidence at a glance

• Trials: 12 trials of one strain during antibiotics pooled in 2015 (1,499 people); eczema-prevention trials of 107, 474 and 184 infants; one gastroenteritis trial of 971 children; one three-week tolerance trial at 100 billion a day.
• Largest single trial: 971 children aged 3 months to 4 years with acute gastroenteritis, 5 days, followed for a month.
• Strongest measured outcome: antibiotic-associated diarrhoea in children, relative risk 0.48 (five trials, 445 children, moderate-quality evidence).
• Not tested in any trial we found: whether a product naming L. rhamnosus without a strain gives the results of the trialled strains.

Sources checked on 16 October 2026.

What is Lactobacillus rhamnosus good for?

Three outcomes have trials, each below: diarrhoea during antibiotics in children, eczema when the mother takes it before and after the birth, and a stomach bug, where it made no difference. The bacterium itself is a lactic acid bacterium used in supplements and added to some fermented foods. Since 2020 its formal name has been Lacticaseibacillus rhamnosus: that year the genus Lactobacillus, then 261 species, was split into 25 genera on whole-genome evidence, and L. rhamnosus moved with L. casei and L. paracasei into the new genus. The bacterium and its trials are unchanged, and "lactobacilli" remains the group word.¹

Does Lactobacillus rhamnosus help with diarrhoea during antibiotics?

In children, one strain did. A 2015 pooled analysis of 12 randomised trials in 1,499 people found that the strain, taken alongside antibiotics, reduced antibiotic-associated diarrhoea from 22.4% to 12.3% (relative risk 0.49, low-quality evidence). Split by age, the difference was significant in children (five trials, 445 children, relative risk 0.48, moderate quality) but not in adults (six trials, 863 adults, relative risk 0.48 with a confidence interval of 0.20 to 1.15), apart from adults on antibiotics to clear Helicobacter pylori, where it was (relative risk 0.26).² Across all live cultures, the 2019 Cochrane review of 33 children's trials found diarrhoea in 8% against 19% on placebo, and 5 billion a day or more did better than less.³ Antibiotics are the treatment for the infection; when to start the cultures is on live cultures and antibiotics.

Does Lactobacillus rhamnosus help with eczema?

The findings depend on who took it and when. In a Finnish trial of 107 at-risk infants, mothers took one L. rhamnosus strain before the birth and the babies for six months afterwards; at four years, 14 of 53 children in the culture group had eczema against 25 of 54 on placebo (relative risk 0.57).⁴ In a New Zealand trial of 474 infants, a different L. rhamnosus strain given from 35 weeks of pregnancy, then to the baby to age two, roughly halved eczema (hazard ratio 0.51); a bifidobacterium strain in the same trial did not (0.90).⁵ In a US trial of 184 high-risk infants given the Finnish strain for their first six months only, with no dosing of the mother, eczema by age two was 28.7% against 30.9% (hazard ratio 0.95).⁶

Across all live cultures, a 2025 Cochrane review of 18 trials in 3,494 infants put eczema by age two at relative risk 0.87, low certainty, and 0.86 and not significant in the trials at low risk of bias.⁷ For eczema that already exists, a 2018 Cochrane review of 39 trials in 2,599 people found little or no difference in symptoms,⁸ and the NHS says "there's no evidence to suggest that probiotics can help treat eczema".⁹ Anything taken in pregnancy goes through a midwife or GP; skin questions more broadly are on are live cultures good for skin.

Does Lactobacillus rhamnosus help with a stomach bug?

Not in the largest trial. In 971 children aged three months to four years with acute gastroenteritis at US emergency departments, five days of the Finnish strain at 10 billion twice a day gave moderate-to-severe illness in 11.8% against 12.6% on placebo (relative risk 0.96), with no difference in how long diarrhoea lasted (median 49.7 against 50.9 hours); the trial was publicly funded.¹⁰ For travellers' diarrhoea, a 2019 analysis by strain found a trend with the same strain that did not reach significance (P = 0.08).¹¹

Which trials used Lactobacillus rhamnosus?

Is Lactobacillus rhamnosus safe to take every day?

For healthy adults the record says yes. In a three-week randomised trial, 17 volunteers took 100 billion live cells of one L. rhamnosus strain a day, against 17 on placebo, with no change in gut symptoms, stool habit or liver and kidney blood tests, and no serious adverse events.¹² Across 36 randomised trials in 9,312 adults on antibiotics, live cultures of all kinds caused no more adverse events than placebo (relative risk 1.00).¹³ How long to take any live culture is on how long to take live cultures.

The caution is for a different population. In a Finnish series of 89 patients with lactobacilli in their blood, the species was identified in 47 cases and 25 of those were L. rhamnosus; in 11 the strain was identical to a widely used supplement strain. 82% of the patients had severe or fatal underlying disease, and the predisposing factors were immunosuppression, long hospital stays and surgery.¹⁴ The NHS says anyone with an existing health condition or a weakened immune system should talk to a doctor before taking live cultures.⁹ The groups are on who should take care with live cultures, and the case series on what disease Lactobacillus causes.

Is Lactobacillus rhamnosus good for women?

None of the trials on this page measured the vaginal flora. Whether a swallowed capsule changes the vaginal flora has been studied strain by strain; those studies are on live cultures and the vaginal flora, with the flora itself on what intimate flora is. Antibiotics and antifungals are the treatments for bacterial vaginosis and thrush.

What we don't know

• No trial has tested a product listing "L. rhamnosus" without a strain against the strains in these trials.
• Adult antibiotic-associated diarrhoea: the strain analysis of six trials in 863 adults did not reach significance, so the adult effect is unsettled.²
• No trial has compared the Finnish and New Zealand strains head to head for eczema.

Frequently asked questions

What is the difference between rhamnosus and acidophilus?

Two species that since 2020 sit in different genera.¹ L. rhamnosus has the larger single-strain trial record; L. acidophilus appears mostly in mixtures. The acidophilus trials are on what acidophilus is good for. The third species people ask about, L. reuteri, has its best trials in infant colic and in bone density in older women; they are on what Lactobacillus reuteri does.

What foods contain Lactobacillus rhamnosus?

Yoghurts, fermented milks and drinks to which a strain has been added and named on the label; it is not a standard yoghurt starter. The fermented foods by species are on what foods are high in Lactobacillus.

Can children take Lactobacillus rhamnosus?

Most of its trials were in children, from newborns to pre-schoolers, at 10 to 20 billion a day.^{4, 6, 10} Anything given to a child goes through a health visitor, pharmacist or GP first.

Sources

1. Zheng J, et al. A taxonomic note on the genus Lactobacillus: description of 23 novel genera. Taxonomic study, 261 species. International Journal of Systematic and Evolutionary Microbiology, 2020. PubMed 32293557.
2. Szajewska H, Kołodziej M. Alimentary Pharmacology and Therapeutics, 2015. Pooled analysis of one Lactobacillus rhamnosus strain and antibiotic-associated diarrhoea, 12 randomised trials, 1,499 people. PubMed 26365389.
3. Guo Q, et al. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane review, 33 randomised trials, 6,352 children. Cochrane Database of Systematic Reviews, 2019. PubMed 31039287.
4. Kalliomäki M, et al. Probiotics and prevention of atopic disease: 4-year follow-up of a randomised placebo-controlled trial. Randomised trial, 107 infants, 4 years. Lancet, 2003. PubMed 12788576.
5. Wickens K, et al. A differential effect of 2 probiotics in the prevention of eczema and atopy. Randomised trial, 474 infants, 2 years. Journal of Allergy and Clinical Immunology, 2008. PubMed 18762327.
6. Cabana MD, et al. Early probiotic supplementation for eczema and asthma prevention: a randomized controlled trial. Randomised trial, 184 infants, followed to age 5. Pediatrics, 2017. PubMed 28784701.
7. Wang HZ, et al. Probiotics in infants for prevention of allergic disease. Cochrane review, 24 randomised trials, 7,077 mother-infant pairs. Cochrane Database of Systematic Reviews, 2025. PubMed 40511642.
8. Makrgeorgou A, et al. Probiotics for treating eczema. Cochrane review, 39 randomised trials, 2,599 people. Cochrane Database of Systematic Reviews, 2018. PubMed 30480774.
9. NHS. Probiotics. nhs.uk/conditions/probiotics. Page last reviewed 24 November 2022 (review overdue).
10. Schnadower D, et al. New England Journal of Medicine, 2018. Randomised trial of one Lactobacillus rhamnosus strain against placebo for acute gastroenteritis, 971 children, 5 days; publicly funded. PubMed 30462938.
11. McFarland LV, Goh S. Are probiotics and prebiotics effective in the prevention of travellers' diarrhea. Pooled analysis by strain, 12 randomised trials. Travel Medicine and Infectious Disease, 2019. PubMed 30278238.
12. Wind RD, et al. British Journal of Nutrition, 2010. Randomised tolerance trial of one Lactobacillus rhamnosus strain at 100 billion a day, 34 healthy volunteers, 3 weeks; authors at a food company's research centre. PubMed 20691131.
13. Liao W, et al. Probiotics for the prevention of antibiotic-associated diarrhea in adults. Pooled analysis, 36 randomised trials, 9,312 people. Journal of Clinical Gastroenterology, 2021. PubMed 33234881.
14. Salminen MK, et al. Clinical Infectious Diseases, 2004. Case series of Lactobacillus bacteraemia, 89 patients, Finland. PubMed 14679449.

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