Lactobacillus reuteri
Lactobacillus reuteri is a lactic-acid bacterium with the most consistent published evidence for one specific clinical application: the strain L. reuteri DSM 17938 in breastfed infants with colic. As with all probiotics, the evidence is for specific named strains, not for the species name on its own.
Camden Medicals editorial · Last reviewed 27 April 2026 · Next review April 2027
- Cross-checked against
- NHS
- NICE
- BNF
- EFSA
- FSA
Camden's editorial team independently graded each health claim below on the strength of the published evidence — see the grade beside every condition.
- Class
- Probiotic
- Typical daily dose
- Infant colic trials use 10⁸ CFU/day (5 drops of standard formulations). Adult formulations are often 10⁸ to 10⁹ CFU/day.
- Top use evidence
- Moderate
On this page
What it is
Lactobacillus reuteri is a Gram-positive, rod-shaped lactic-acid bacterium first isolated from human breast milk and the gastrointestinal tracts of mammals and birds. Unlike many Lactobacillus species, some L. reuteri strains produce reuterin — an antimicrobial compound active against bacteria, yeasts, and protozoa — from glycerol metabolism in the gut.
The most-trialled commercial strain is L. reuteri DSM 17938 (Bio-Gaia), which is supplied in oral drops formulated for infant colic and as adult-format capsules and chewables. Other strains include L. reuteri ATCC PTA 6475 (also from Bio-Gaia, more often studied in adult bone-density and oral-health work).
At a glance
- A lactic-acid bacterium found naturally in some human and animal guts.
- Most-studied clinical use: L. reuteri DSM 17938 in breastfed infants with colic — multiple positive RCTs.
- Evidence weaker in formula-fed infants and in adult indications.
- No GB-authorised health claim for the species generically.
- Same probiotic safety cautions apply as for other Lactobacillus species — see safety section.
What people use it for
Breastfed infants with colic
L. reuteri DSM 17938 has multiple positive randomised trials in breastfed infants with colic, with reductions in average daily crying time of around 30-50 minutes versus placebo. Talk to a GP, health visitor, or pharmacist before giving to a baby. [2,5,6]
Some evidenceModerateFormula-fed infants with colic
Trials in formula-fed infants have shown smaller and less consistent benefits than in breastfed infants. The mechanism may involve infant-microbiome differences between feeding routes.
Some evidenceLimitedAdults with functional gastrointestinal symptoms (IBS, constipation)
Smaller trials with mixed results across these indications. Not a first-line UK guideline recommendation.
Some evidenceLimitedAdults with periodontitis or gingivitis (oral chewable formulations)
Some adult-format L. reuteri products are marketed for oral health (gum inflammation, breath). Trial evidence is mixed; these uses are NOT a substitute for dental hygiene and routine dental check-ups.
Some evidenceLimited
How it works
L. reuteri produces lactic acid, acetic acid, and (in some strains) reuterin and reutericyclin — antimicrobial compounds that may inhibit enteric pathogens. Specific strains influence intestinal motility and visceral pain signalling, which is the mechanistic story behind the infant-colic indication. The gut-brain axis research has highlighted L. reuteri among probiotic candidates for mood and anxiety in animal studies; human translation is early and there is no GB-authorised mood claim.
Common myths
Myth"L. reuteri colic drops are a "must-have" for every baby"
RealityColic affects up to ~20% of infants and resolves spontaneously by ~3-4 months in nearly all cases. The trial evidence supports modest crying-time reduction in breastfed infants with diagnosed colic — not routine prophylaxis for all babies. Talk to your GP or health visitor before starting any infant supplement.
Myth"L. reuteri lactates strain identifier is the same as the colic strain"
RealityL. reuteri DSM 17938 (the colic strain) and L. reuteri ATCC PTA 6475 (more often studied in adult bone-density / oral-health work) are different strains. Trial evidence does not transfer between them.
Common online questions
Synthesised from the questions UK shoppers most often ask online about Lactobacillus reuteri. Each answer is editorial and links to its evidence in the Sources list below.
Will probiotic drops cure my baby's colic?
For breastfed infants with diagnosed colic, L. reuteri DSM 17938 has reduced average daily crying by around 30-50 minutes in positive trials. That is meaningful but modest — colic typically resolves on its own by 3-4 months regardless. Talk to your GP or health visitor first; persistent or severe infant crying warrants medical assessment to rule out other causes. [2]
Can I give L. reuteri to a formula-fed baby with colic?
Trial evidence is weaker in formula-fed infants — some studies show small benefit, others none. The breastfed-vs-formula difference may relate to differences in the infant gut microbiome by feeding route. Talk to your GP or health visitor.
Should I take L. reuteri for IBS?
Possibly — NICE CG61 lists probiotics as one option to trial for at least 4 weeks. For L. reuteri specifically the adult IBS evidence is limited. Bifidobacterium longum 35624 has stronger published evidence for adult IBS specifically. [3]
Is L. reuteri safe long-term?
For most healthy adults, yes — at typical food-supplement doses L. reuteri has a long safety record. As with all probiotics, immunocompromise, critical illness, and central venous catheters change the risk-benefit calculation. Long-term routine use without a specific indication is not well-evidenced.
Are L. reuteri drops vegetarian / vegan?
The bacterium itself is not animal-derived. Some commercial L. reuteri drops are formulated in oil bases that may be animal-derived; check the label. Capsule formulations may use gelatin or HPMC — read the ingredient list.
Camden guides citing Lactobacillus reuteri
Editorial pieces from the Camden blog that reference Lactobacillus reuteri. Each guide cites the evidence it draws on.
🔬 Camden’s evidence review
The research Camden reviewed, graded on its strength. This is our own appraisal — it sits beneath the official guidance above, never above it.
Infant colic in breastfed infants — L. reuteri DSM 17938
ModerateEvidencemoderateMultiple positive RCTs (Savino 2007, 2010, Indrio 2014 for prevention work) and a 2014 meta-analysis support L. reuteri DSM 17938 in exclusively-breastfed infants for reducing daily crying time. The Sung 2014 BMJ trial in mixed-feeding infants was negative — reinforcing that the effect is most consistent in breastfed infants specifically. [2,7,5]
Functional constipation in children
LimitedEvidencelimitedSome paediatric trials of L. reuteri in chronic functional constipation have shown modest improvements; not standard of care in NICE guidance.
Adult IBS / functional bowel symptoms
LimitedEvidencelimitedSmaller adult trials; mixed results. NICE CG61 lists probiotics as one option to trial; L. reuteri is among the species studied but not the most-evidenced for adult IBS. [3]
Safety
Lactobacillus reuteri has a long safety record at typical doses for healthy adults and term infants. NOT appropriate for everyone — see scenarios below. Infant use should always involve a GP or health visitor.
Talk to your pharmacist or GP first if you:
- You are buying for an infant — see your GP or health visitor first; persistent infant crying or other symptoms need medical assessment.
- You are immunocompromised, on chemotherapy, or have a low CD4 HIV count.
- You are critically ill or have a central venous catheter.
- You have severe acute pancreatitis.
- You are pregnant or breastfeeding.
Common side effects: Generally very well tolerated. Mild bloating or wind in the first few days; settles with continued use.
Pregnancy and breastfeeding
Some research-context use in pregnancy. Talk to your midwife or pharmacist.
Same framing.
Talk to your GP, midwife, or pharmacist before starting any supplement during pregnancy or breastfeeding.
More clinical detail (for clinicians and informed readers)
Contraindications
- Severe immunocompromise.
- Critical illness with central venous access.
Drug interactions
- Antibiotics — separate doses by at least 2 hours.
- Immunosuppressants — caution per the contraindications.
This is not an exhaustive list. Always tell your prescriber and pharmacist about every supplement you take.
Common side effects
- Mild bloating or flatulence.
Rare side effects
- Bacteraemia in immunocompromised or critically-ill patients (rare).
How to take it
- Typical supplemental range
- Infant colic trials use 10⁸ CFU/day (5 drops of standard formulations). Adult formulations are often 10⁸ to 10⁹ CFU/day.
- Timing
- No specific timing requirement.
How to spot quality
Look for
- Named strain identifier (L. reuteri DSM 17938 for colic; L. reuteri ATCC PTA 6475 for adult use cases).
- CFU per dose stated AT END OF SHELF LIFE.
- Cold-chain shipping where applicable; check storage instructions.
Red flags
- Generic "L. reuteri" without strain identifier.
- Marketing claims about "treating colic" rather than "supporting reduced crying time" in studied populations.
Commonly combined with
Other ingredients that share a biological pathway, cofactor relationship, or evidence-backed protocol with this one. Mechanisms below cite primary physiology — not folk pairing. Doses are literature ranges, not recommendations. Talk to your pharmacist or GP before changing your stack, especially if you take prescription medication.
Lactobacillus rhamnosus
Moderate evidenceLactobacillus cluster — most-trialled lactobacillus strains. Both have AAD-prevention + paediatric trial bodies.
L. rhamnosus GG + L. reuteri DSM 17938 — different strains, overlapping AAD-prevention + paediatric-acute-gastroenteritis evidence. Combination products extend strain coverage.
Evidence: Cochrane probiotic-AAD support; Camden lactobacillus-rhamnosus covers detail. [8,9,10]
Doses studied: 10⁹-10¹⁰ CFU each strain daily during antibiotic course + 1-2 weeks after.
Saccharomyces boulardii
Limited evidenceAAD-prevention cluster — different organism domains (yeast vs lactic-acid bacterium).
S. boulardii antibiotic-resistant yeast + L. reuteri lactobacillus. Mechanism complementary; both have AAD prevention + paediatric evidence.
Evidence: Camden saccharomyces-boulardii covers cluster.
Doses studied: S. boulardii 250-1000 mg + L. reuteri 10⁸-10⁹ CFU daily.
Bifidobacterium longum
Limited evidenceMulti-strain microbiome cluster — Lactobacillus + Bifidobacterium genus complementarity.
L. reuteri small-intestinal colonisation; B. longum colonic colonisation. Different gut-region niche distribution; mechanism complementary.
Evidence: Multi-strain microbiome support.
Doses studied: 10⁹-10¹⁰ CFU each strain daily.