Lactobacillus reuteri
Best for
Reduce diarrhea
Proven benefit 100000000 mg/kg/day/day 4 weeks 1 meta-analysis, n=764 #2 of 16 studied
- 3 papers
- 1 of 2 outcomes
- 1 positive
Lactobacillus reuteri shortens acute diarrhea episodes in young children, providing a proven benefit that does not establish the same result for adults or every cause.
Median effective dose, most-studied outcomes
- Ease diarrhea symptoms 100,000,000 mg/kg/day 4 wk
Risk, worst reported severity
- amoxicillin-clavulanate minor
- pantoprazole minor
What lactobacillus reuteri actually does
| Outcome | Effect | Evidence | Dose | Time | Rank |
|---|---|---|---|---|---|
| Clear benefits 1 | |||||
| Reduce diarrhea Proven benefit Diarrhea brings loose, watery stools that can disrupt daily life and cause dehydration. | | 1 meta-analysis 2 papers · n=764 | 100000000 mg/kg/day | 4 wk | #2 /16 |
Effect tiers come from native-unit MCID where available, Cohen's d otherwise.
Dose, timing & forms
How much
For acute diarrhea symptoms, the reviewed trials used an oral daily protocol reported as 10^8 mg/kg/day for about 4 weeks.1 That unit is unusual for a live probiotic, since labels usually list colony-forming units rather than milligrams. Match the exact strain and serving instructions on the product label rather than trying to convert that research entry yourself.1
When and how long
Use it consistently each day during the studied course, rather than treating it like an occasional rescue product.1 The diarrhea trial literature does not establish that morning versus evening dosing changes results.1 If you also use amoxicillin-clavulanate, check with a pharmacist or clinician because the antibiotic can reduce the probiotic's effect.
Forms & standardisation
Look for the full strain identifier, not just the words "Lactobacillus reuteri." The pediatric acute-diarrhea evidence came from a defined L. reuteri preparation, and probiotic benefits do not automatically transfer from one strain or product format to another.1 A label that states the strain, viable count through expiration, and storage instructions gives you a more research-matched starting point.
Studied range, by outcome
| Outcome | Studied range | Median effective | Duration | Evidence |
|---|---|---|---|---|
| Ease diarrhea symptoms | 100,000,000 mg/kg/day | 100,000,000 mg/kg/day | 4 wk | 2 papers 1 sig. endpoint |
Adverse events and drug interactions
Drug interactions
What this is and how it works
- Across 2 studies (n=764), Lactobacillus reuteri shortened acute diarrhea episodes in young children.1
- Three papers reviewed here span 2 outcomes, with evidence concentrated on acute diarrhea episodes.
- Evidence applies to specific preparations in children and does not establish benefits for adults or every diarrhea cause.
Lactobacillus reuteri is a live bacterium that naturally turns up in the human gut and other parts of the body. Supplement makers grow selected strains, freeze-dry them, and package them as capsules, powders, or drops. The strain is the important part: two products with the same species name can act more like cousins than identical twins.1
L. reuteri produces substances such as reuterin and competes with other microbes for space and fuel in the gut. Picture it as adding a well-behaved vendor to a crowded market: it takes up a stall and changes what nearby vendors can sell, which can make the gut environment less friendly to some unwanted microbes.1 Clinical diarrhea trials show the outcome, but they do not prove that any single mechanism explains it.1
Bottom line
Lactobacillus reuteri makes the most sense for a parent discussing a strain-specific probiotic alongside standard hydration for a child's acute diarrhea. The benefit is meaningful but rests on a small evidence base, and the direct trial evidence does not establish the same result for adults or every diarrhea cause.1 Skip self-treatment and seek medical care for bloody stool, severe dehydration, high fever, or symptoms that persist.
Common questions
Does Lactobacillus reuteri stop diarrhea?
Which Lactobacillus reuteri strain is best for diarrhea?
Can adults take Lactobacillus reuteri for diarrhea?
Should you take Lactobacillus reuteri with antibiotics?
Sources
Sources
Generated August 27, 2026
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