Know2eat

Lactobacillus reuteri

Limosilactobacillus reuteri

Probiotics & Gut

What lactobacillus reuteri may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedDigestive comfortModerate evidence· 3 sources

Then, in order

About Lactobacillus reuteri

A lactobacillus native to the human gut and breast milk. The most-studied strain, DSM 17938, is a derivative of an isolate from the breast milk of a Peruvian mother and is used mainly in infants.

L. reuteri DSM 17938 is the clearest example of a probiotic whose evidence depends not just on the strain but on the population. An individual-participant-data meta-analysis of infant colic trials found a substantial reduction in crying time in exclusively breastfed infants and essentially no effect in formula-fed infants — the same organism, the same dose, opposite conclusions depending on what the baby was drinking. Other strains sold under this species name, including one studied for LDL cholesterol, have their own separate and much smaller evidence bases.

Sold as
Oil drops, Chewable tablet, Sachet, Capsule
Standardised to
CFU of the named strain, commonly 100 million CFU per five drops for DSM 17938 — a product without this marker may not resemble what was studied.
Also known as
L. reuteri, DSM 17938, Protectis

Regulation: Sold as a food supplement or food for special medical purposes depending on the market, with no pre-market efficacy review as a supplement. EFSA has not authorised probiotic health claims in the EU.

What the research used

The amounts, forms and durations published trials of Lactobacillus reuteri actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Infant colic

    100 million CFU

    Moderate

    Oil drops, once daily · 21–28 days

    Individual-participant-data analysis found benefit confined to exclusively breastfed infants; formula-fed infants showed no effect. Dosing outside infancy is not established from this literature.

  • Studied for LDL cholesterol (strain NCIMB 30242)

    2–3 billion CFU

    Limited

    Capsule, twice daily · 9 weeks

    A different strain entirely, studied by the company that owned it, reporting LDL reductions of around 9–12%. Independent replication is lacking and the result does not transfer to DSM 17938.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

  • With food

    Not enough

    Infant drops are typically given with a feed. For the cholesterol strain, dosing with meals was part of the protocol because bile salt hydrolase activity acts on bile acids released in response to eating — a mechanistic reason rather than a tested comparison.

    Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

The evidence in depth

Best supported: Moderate

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Digestive comfort

Gut & Digestive Health
Moderate evidence

Pooled individual-participant data from infant colic trials show reduced crying time with L. reuteri DSM 17938 in exclusively breastfed infants, with no detectable benefit in formula-fed infants. It is an unusually clean demonstration that a probiotic effect can depend on the host context.

Moderate evidence. Several human studies point the same way, with real caveats.

View the 3 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Blood lipid profile

Heart Health
Limited evidence

Trials of the specific strain NCIMB 30242 report reductions in LDL cholesterol, attributed to bile salt hydrolase activity increasing bile acid excretion. The work comes almost entirely from one group with a commercial interest and has not been independently replicated.

What may be going on: Bacterial bile salt hydrolase deconjugates bile acids, reducing their reabsorption and increasing hepatic use of cholesterol to replace them.

Limited evidence. Early human work, or mostly lab and animal research.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Immune function

Immune Health
Not enough evidence

Studies of L. reuteri and infection rates in children and adults are small and inconsistent. There is not enough evidence to support an immune claim for any strain of this species.

Not enough evidence. Not enough human research to say anything useful yet.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Avoid

    Immunocompromise, central lines and critical illness

    Live cultures are not appropriate for critically ill, severely immunosuppressed or central-line patients without specialist advice, including in neonatal intensive care where the balance of evidence for probiotics is genuinely contested and cases of sepsis attributable to supplement organisms have been reported.

  • Worth knowing

    The effect depends on the infant’s feeding

    Benefit in colic trials was confined to exclusively breastfed infants. Giving it to a formula-fed infant is doing something the pooled evidence says does not work, which is worth knowing before spending money on it.

  • Worth knowing

    Strain substitution

    DSM 17938 and NCIMB 30242 are different organisms with different evidence. A product labelled only "L. reuteri" carries neither result automatically.

  • Allergy

    Carrier oils in infant drops

    Drops are suspended in sunflower or medium-chain triglyceride oil with added ingredients that vary by market. Checking the excipient list matters for infants with known sensitivities.

Evidence ratings on this page: 1 moderate evidence, 1 limited evidence, 1 not enough evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take Lactobacillus reuteri, or a dose to follow.