L. reuteri DSM 17938 for Colic: What the Actual Trial Found

The 74% figure, sourced properly

You have probably seen some version of this claim: a specific probiotic strain reduces colic crying by 74%. It traces back to one real, findable trial: Savino et al., "Lactobacillus reuteri DSM 17938 in Infantile Colic: A Randomized, Double-Blind, Placebo-Controlled Trial," Pediatrics, 2010. Worth reading what it actually did, rather than just repeating the headline number.

What the trial actually tested

The trial enrolled exclusively breastfed infants meeting the Wessel criteria for colic, the standard clinical definition (crying for more than three hours a day, more than three days a week, for more than three weeks, in an otherwise healthy, well-fed infant). Infants were randomized to receive either L. reuteri DSM 17938 at a dose of 10⁸ colony-forming units daily, delivered in five drops, or a placebo, for 21 days.

By day 21, the treatment group showed a median reduction in daily crying time from roughly 370 minutes to roughly 35 minutes. The placebo group's reduction was smaller and slower. That gap, the difference in how much and how fast crying time dropped, is where the 74% figure comes from.

What it does not tell you

It was conducted in breastfed infants specifically. This is the single most important caveat and the one most often dropped when the finding gets repeated online. If your baby is formula-fed or mixed-fed, this trial's population does not match yours, and the mechanism, timing, and even the specific strain's behavior in a different feeding context have not been established by this study. A separate, broader evidence base covers formula-feeding, and it is not this trial.

It tested one specific strain, at one specific dose. "Probiotic" is not a single thing. Strain specificity is the entire point: L. reuteri DSM 17938 is a particular, patented strain (the commercial product built around it is BioGaia Protectis), and the trial's results do not generalize to "a probiotic" in the way marketing for other probiotic products sometimes implies.

It is one trial, not the entire evidence base. Two independent systematic reviews, Ellwood, Draper-Rodi and Carnes, BMJ Open, 2020, and Hjern, Lindblom, Reuter and Silfverdal, Acta Paediatrica, 2020, both reached broadly consistent conclusions reviewing the wider literature. Consistency across independent reviews matters more than any single trial, however well-designed that trial was.

Why strain specificity matters more than the word "probiotic"

Colic-specific clinical evidence exists for this exact strain, at this dose, in this population. It does not exist, at anywhere near the same strength, for "a probiotic" as a category. A generic multi-strain probiotic bought because the label says "supports digestive health" has not been through the same colic-specific trial process, and treating the category as interchangeable with the specific, studied strain is a common and understandable mistake, not a small one.

Where this fits into a bigger picture

Gut microbiome imbalance is one of three root causes behind colic presentations, alongside nervous system dysregulation and acoustic overload. This trial, and the strain it studied, addresses the gut system specifically. It has very little to say about a baby whose primary driver is nervous system dysregulation or acoustic mismatch, and applying a gut-targeted intervention to a baby whose primary system is something else is a common reason a well-evidenced intervention still doesn't seem to work.

That is a diagnostic question, not an evidence question, and it is worth answering before deciding whether this specific research is even the relevant piece of evidence for your own situation.