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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

L. reuteri

The Strain Behind a Yogurt Craze

Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.

40 human trials, about 200 studies, >10,000 participants. The written rationale for this grade is still being prepared.

FDA
GRAS; in various products
WADA
Not prohibited

Reference only. Not medical advice.

What can go wrong

The studied strains are generally safe in healthy people and hold FDA GRAS and EU QPS status. Risks concentrate in specific situations: rare invasive infections (bacteremia) have been reported in immunocompromised patients and preterm or critically ill infants, so live cultures warrant caution in those groups. The viral homemade yogurt fermented for long periods can grow unwanted organisms if hygiene is imperfect, and its high-count, exotic anti-aging claims are untested in humans. Infant colic, pediatric use, and pregnancy are sensitive contexts: parents and patients should discuss any probiotic, dose, or feeding decision with a qualified pediatrician or clinician rather than acting on a social-media protocol. The evidence is strain-specific; a viral yogurt is not the studied clinical product.

Lactobacillus reuteri (reclassified Limosilactobacillus reuteri in 2020) is a genuinely well-studied probiotic whose strongest human evidence is narrow and population-specific: strain DSM 17938 is associated with reduced crying and fussing in colicky BREASTFED infants, while the same strain showed no significant benefit in formula-fed infants in the pooled Sung analysis. It also has mixed evidence in oral health and some gut applications. From roughly 2023 to 2025 it became a viral phenomenon when cardiologist-author William Davis promoted homemade high-count 'L. reuteri yogurt' with sweeping claims about deep sleep, younger skin, oxytocin, and aging. Those longevity claims rest largely on mouse studies from an MIT group and are not established in humans, and long home fermentation carries contamination risk. The strain is real and the colic signal is real; the yogurt hype outruns the data.

A well-studied strain with real evidence for infant colic, recently the center of a viral "L. reuteri yogurt" longevity craze.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Associated with reduced crying and fussing in colicky BREASTFED infants (DSM 17938)
  • Mixed evidence in oral health (DSM 17938 with ATCC PTA 5289, marketed as Prodentis)
  • Some gut-health applications studied (for example antibiotic-associated diarrhea, functional GI symptoms)
  • A case study in strain-specific, population-specific evidence versus viral hype

What people get wrong

  • Often said'L. reuteri yogurt' reverses aging, deepens sleep, and boosts oxytocin in people

    ActuallyThese viral claims are not established in humans. The oxytocin, wound-healing, thicker-fur, and youthful-testosterone findings come from mouse studies by an MIT group (Poutahidis and Erdman, PLoS ONE 2013-2014). No human trial has shown the homemade yogurt reverses aging.

  • Often saidL. reuteri helps all colicky babies equally

    ActuallyThe pooled Sung 2018 analysis found DSM 17938 was associated with reduced crying in BREASTFED infants (number needed to treat 2.6) but showed no significant benefit in formula-fed infants. The effect is population-specific.

  • Often saidHomemade high-count reuteri yogurt equals the studied clinical probiotic

    ActuallyStrain identity, dose, and formulation differ from the tested product, and long home fermentation can culture contaminants if hygiene slips. The viral yogurt is not the intervention that was studied in the colic trials.

  • Often saidRegulators have endorsed reuteri for oral or gum health

    ActuallyEFSA's panel concluded in 2020 that the evidence was insufficient to establish a cause-and-effect relationship between DSM 17938 plus ATCC PTA 5289 lozenges and normal gum function. The oral-health evidence remains mixed.

Who profits, and who pushes back

  • Valerie Sung and colleagues

    Pushes backLead authors, individual-participant-data meta-analysis of L. reuteri for colic (Pediatrics, 2018)

    L reuteri DSM17938 is effective and can be recommended for breastfed infants with colic. Its role in formula-fed infants with colic needs further research.

  • EFSA NDA Panel

    Pushes backEuropean Food Safety Authority scientific panel (2020 opinion)

    The evidence provided is insufficient to establish a cause and effect relationship between the consumption of orodispersible lozenges containing L. reuteri DSM 17938 and L. reuteri ATCC PTA 5289 and maintenance of normal gum function.

  • Dr. William Davis

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes it"Super Gut" author

    Popularized the viral homemade "L. reuteri yogurt" with broad anti-aging/wellbeing claims and related books and programs.

  • BioGaia

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itReuteri product maker

    Markets clinically studied DSM 17938 products (e.g. for infant colic); the legitimate evidence base sits here, not in the yogurt trend.

  • Pediatric researchers

    Promotes itColic trials

    Provide the genuine evidence, mainly reduced crying in breastfed colicky infants with specific strains.

Where the research comes from

Share of published research by country of origin.
PlaceShare of published research
Europe34%
USA32%
Asia20%
Other14%

Research published from: Global.

How we got here

Gerhard Reuter, a German microbiologist, described this organism in the human gut and feces in the 1960s, initially grouping it within Lactobacillus fermentum before it was recognized as a distinct species and named Lactobacillus reuteri in his honor in 1980. It is an ancient, host-adapted symbiont found across the guts of humans and many animals worldwide, and human-derived lineages were later isolated by researchers including work associated with a Peruvian mother's breast-milk isolate that became the widely studied strain DSM 17938. In 2020 a large phylogenetic revision (Zheng and colleagues) split the genus Lactobacillus and reclassified this species as Limosilactobacillus reuteri. Its modern evidence base grew mainly in the 2010s around infant colic. From about 2023 to 2025 it entered wellness virality when William Davis popularized a homemade high-count yogurt with expansive anti-aging claims, turning a narrowly studied strain into a social-media sensation.

  1. 1960sGerhard Reuter isolates and describes the organism in human gut and feces
  2. 1980Recognized as a distinct species and named Lactobacillus reuteri
  3. 2008FDA issues no-questions GRAS response for BioGaia's DSM 17938 (GRN 254)
  4. 2013-2014MIT group (Poutahidis, Erdman) publishes mouse studies linking L. reuteri to oxytocin, wound healing, thicker fur, and youthful testosterone
  5. 2018Sung individual-participant-data meta-analysis: DSM 17938 helps breastfed colicky infants, not formula-fed
  6. 2020Genus reclassification to Limosilactobacillus reuteri; EFSA rejects the oral-lozenge gum-function health claim
  7. 2023-2025William Davis popularizes homemade 'L. reuteri yogurt'; viral longevity craze
  8. OngoingEvidence-vs-hype gap widely debated

At a glance

Best evidence
Infant colic (breastfed infants)
Key strains
DSM 17938, ATCC PTA 6475
Viral trend
Homemade "reuteri yogurt"
Trend claims
Outrun the evidence

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about L. reuteri. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.

Sources