Lactobacillus reuteri DSM 17938 is one of the most widely studied probiotic strains, with research syntheses evaluating its effects across 6 health outcomes. The strongest and most consistent evidence supports its use for reducing crying time in infants with colic (7 studies, large effect size) and for reducing abdominal pain in children with functional gastrointestinal disorders (11 studies, moderate evidence strength). Studies most frequently use doses around 10⁸ CFU per day, predominantly in pediatric populations.
Strongest evidence The largest body of research supports reduced crying time in breastfed infants with colic (6 of 7 studies beneficial; large effect size; 10⁸ CFU/day) and reduced abdominal pain in children with functional abdominal pain or IBS-D (9 of 11 studies beneficial; moderate evidence; 10⁸ CFU/day). For reduced diarrhea rate (5 of 8 studies beneficial) and reduced duration of diarrhea (5 of 5 studies beneficial), evidence is moderate, with doses ranging from 1×10⁸ to 2×10⁹ CFU/day in pediatric acute gastroenteritis.
Mixed or weaker evidence Evidence for reduced vomiting frequency (3 studies, all beneficial but small effect, low evidence) and reduced stool volume (1 of 3 studies beneficial, low evidence) is preliminary. Results for stool volume are largely neutral in children with functional constipation, and the vomiting data come from small infant studies with inconsistent dosing.
Effective dose patterns Most outcomes converge on a daily dose of 1×10⁸ CFU as the most common effective dose. For diarrhea outcomes, larger doses up to 2×10⁹ CFU/day have been used, but no clear dose-response relationship has been established.
Population insights The evidence overwhelmingly focuses on pediatric populations — infants with colic, children with functional abdominal pain or acute gastroenteritis, and young children in daycare settings. Evidence for adults is limited to one outcome (IBS-D in abdominal pain studies), making adult conclusions preliminary.
Notable caveats Across all outcomes, publication bias is a concern — null results may be underrepresented. Several neutral findings occur in larger, higher-quality trials (e.g., 2 RCTs with evidence score 7 for abdominal pain). Effect sizes vary considerably, and many studies have small sample sizes. The evidence base is small for most outcomes (≤11 studies per outcome).
Across 18 clinical studies, no specific adverse events were associated with increased risk compared to control for Lactobacillus reuteri DSM 17938. In 17 studies that quantitatively tested specific outcomes (e.g., crying time, stool characteristics, growth parameters), no significant differences were found between probiotic and control groups, with several showing statistically significant improvements favoring the probiotic (e.g., reduced colic, fewer hard stools). Additionally, 18 mentions of general tolerability or unquantified safety statements described the probiotic as well tolerated, with no serious adverse events attributed to the intervention.
Caveats: Most studies were in infants and children, and many were relatively short-term; long-term safety data are limited. Studies were primarily designed to evaluate efficacy, and rare adverse events may not have been detected.