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Limosilactobacillus reuteri DSM 17938
The best-evidenced probiotic for infant colic — but specifically in breastfed babies, where an individual-participant meta-analysis found a number-needed-to-treat of 2.6. In formula-fed infants the benefit disappears, and the largest single trial actually favoured placebo. Adult claims mostly belong to different L. reuteri strains entirely.
What the evidence says
Most L. reuteri DSM 17938 studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2010–2023 with a typical study size of 52 participants.
Based on 11 studies · 5 meta-analyses · 6 RCTs · 369 total participants
Confidence
High confidenceBy outcome
For colic in breastfed infants the individual-participant-data meta-analysis is genuinely strong (number needed to treat 2.6), but the largest single trial was null and even favoured placebo, the benefit vanishes in formula-fed infants, and every adult claim belongs to a different L. reuteri strain.
3 trials ongoing or recruiting · 55 completed on ClinicalTrials.gov
6 of the completed trials have posted results
Registered trials show research momentum for L. reuteri DSM 17938, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for L. reuteri DSM 17938 meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“Lactobacillus reuteri DSM 17938 Balances the gut microflora”
“Lactobacillus reuteri lactic acid bacteria Promotes mouth and tooth health”
“Lactobacillus reuteri DSM 17938 Lactobacillus reuteri ATCC PTA 5289 Supports a healthy oral flora”
“Lactobacillus reuteri THT 030803 * Helps to strengthen natural defences * Stimulates immune system * Strengthens resistance of organism”
“Lactobacillus reuteri DSM 17938 Lactobacillus reuteri ATCC PTA 5289 Helps strengthen your body's natural defences Stimulates the immune system”
“Lactobacillus reuteri ATCC 55730 probiotic beneficially affects the intestinal flora supports a healthy intestinal flora balances the intestinal flora”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Our research database did not respond in time, so the studies and count above cover only our curated set. This refreshes automatically.
Limosilactobacillus reuteri DSM 17938 has one unusually well-supported use: treating colic in breastfed infants.
An individual-participant-data meta-analysis pooling raw data from four double-blind RCTs found babies nearly twice as likely to respond by day 21, with a number needed to treat of 2.6 — remarkably strong for a supplement. But the picture is not uniform.
The largest single trial (BMJ 2014, n=167) was null and directionally adverse, with the probiotic group crying 49 minutes MORE per day than placebo, an excess concentrated in formula-fed infants. The IPD meta-analysis reaches the same split: dramatic in breastfed babies, not significant in formula-fed ones.
Cochrane, looking at PREVENTION rather than treatment, found no clear effect and graded all outcomes low certainty with very high heterogeneity. Beyond colic there is moderate evidence for shortening acute childhood diarrhoea and modest evidence for functional abdominal pain in children.
A critical caveat for shoppers: the widely marketed adult claims do not belong to this strain.
The cholesterol-lowering data are for NCIMB 30242, the gum-health data used a two-strain lozenge, and the popular testosterone and oxytocin claims attached to ATCC PTA 6475 rest on rodent work — and where a human trial does exist it is NULL: a 12-week randomised, double-blind, placebo-controlled trial of ATCC PTA 6475 in healthy men aged 55-65 found no effect on testosterone at either dose (PMID 38770015).
Trials measured increased faecal lactobacilli alongside reduced E. coli and ammonia. Not consistently reproduced — the largest trial found no change in faecal microbial diversity or E. coli colonisation.
Faecal calprotectin, a marker of intestinal inflammation, fell significantly alongside reduced crying time in one 30-day Italian trial (P=0.0001). This conflicts with the larger BMJ trial, which found no calprotectin difference versus placebo, so the finding is not established.
In one randomized trial, peripheral-blood FOXP3 messenger RNA rose significantly (P=0.009) and the RORgamma/FOXP3 ratio fell from 0.61 to 0.48 over 30 days (P=0.028) — a shift away from inflammatory Th17 toward regulatory T-cell signalling. Single-trial biomarker evidence, not independently replicated.
L. reuteri converts glycerol into reuterin, a broad-spectrum antimicrobial. Characterised in vitro; not demonstrated in the human gut.
How L. reuteri DSM 17938 works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
The population where benefit is established; the strain has a dedicated phase-1 infant safety trial.
Benefit is not established and one large trial reported more fussing. Not recommended on current evidence.
Pooled data suggest reduced necrotizing enterocolitis and late-onset sepsis, but at very low certainty and underpowered. Neonatal clinical supervision only.
No pregnancy-specific safety trial exists. Discuss with a clinician.
Antibiotics may reduce the organism's viability. No drug-interaction data specific to this strain exists in the published literature.
Tip: Seen in the largest trial, concentrated in formula-fed babies; discontinue if crying worsens
Tip: Avoid live probiotics in these groups without physician oversight
L. reuteri DSM 17938 has an evidence score of 6/10 — moderate evidence based on 58 indexed studies, including 5 meta-analyses. The best-evidenced probiotic for infant colic — but specifically in breastfed babies, where an individual-participant meta-analysis found a number-needed-to-treat of 2.6. In formula-fed infants the benefit disappears, and the largest single trial actually favoured placebo. Adult claims mostly belong to different L. reuteri strains entirely. Representative study: PMID 30865287.
The commonly studied dose of L. reuteri DSM 17938 is 1 x 10^8 CFU daily (5 drops) for infant colic — the dose used in every positive trial. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for L. reuteri DSM 17938 — consistent daily use matters more than the time of day. Trials gave a single daily dose of 5 drops.
L. reuteri DSM 17938 is generally well-tolerated and considered safe for most healthy adults at recommended doses. Reported side effects are uncommon and include increased fussing in formula-fed infants, bloodstream infection in immunocompromised or critically ill patients. Use caution if any of these apply to you: Immunocompromise or immunosuppression; Critical illness; Indwelling central venous catheter.
Probiotics
Likely helpsLive microorganisms where strain selection determines outcome — Lactobacillus and Bifidobacterium strains best studied for gut, immune, and mood.
Saccharomyces Boulardii
Likely helpsAntibiotic-resistant probiotic yeast that supports digestive regularity and gut flora during travel and antibiotic use.
VSL#3 / Visbiome
Mostly mechanism / observationalAn 8-strain blend dosed in the hundreds of billions to trillions of CFU per day — roughly 45 to 7,000 times a typical 1-10 billion CFU consumer probiotic — with the largest effect size in the probiotic literature for one narrow use: maintaining remission in chronic pouchitis after ulcerative colitis surgery. It is null for IBS and Crohn's — and since 2016 the brand name no longer reliably identifies the formulation that was studied.
B. lactis (BB-12 / HN019)
Mostly mechanism / observationalThe most-replicated probiotic effect on gut transit — it measurably speeds things up and adds roughly one bowel movement a week in people who are already low. But it is not a constipation cure: the two largest, best-designed trials both missed their primary endpoints, and the honest effect is hours off transit time, not a fix.
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Reviewed by Dr. Baher Al Hakim · Last reviewed July 2026 · evidence from 11 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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