Lactobacillus reuteri DSM 17938 for Infant Colic: What the RCTs Show

Infant colic affects roughly 20% of newborns. The classic definition — three or more hours of crying per day, three or more days per week, for at least three weeks in an otherwise healthy infant — captures a real distress for both baby and family without identifying a single cause. Decades of trials have looked at hydrolysed formulas, simethicone, dietary elimination in breastfeeding mothers, and probiotics. One probiotic strain has emerged with the most consistent evidence: Lactobacillus reuteri DSM 17938.

The core trial evidence

Five well-conducted RCTs and one large multi-centre study, mostly Italian and European, tested L. reuteri DSM 17938 at five oral drops daily (10⁸ CFU) for 21–28 days in colicky infants. In four out of five studies, breastfed infants on the probiotic showed a significant reduction in daily crying time compared to placebo, with the responder rate (50% reduction in crying time) reaching roughly 70% in the active arm versus 30% in placebo [1]. The strain has been studied in over 800 infants total.

The 2014 Australian outlier

A 2014 Australian RCT by Sung and colleagues (n=167) included both breastfed and formula-fed infants and found no overall benefit from L. reuteri DSM 17938 [2]. The trial reignited debate about whether the European positive trials reflected a true breastfed-only effect or unblinded family expectations. A 2018 individual-participant-data meta-analysis pooling four trials (345 infants) found L. reuteri DSM 17938 reduced crying time only in exclusively breastfed infants, with no clear benefit in formula-fed infants [3].

The current professional position

The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) 2018 position statement on probiotics for paediatric gastrointestinal disorders concluded there was "moderate-quality evidence" supporting L. reuteri DSM 17938 for infant colic in exclusively breastfed term infants [4]. The 2022 ACG paediatric probiotic guidelines and a 2023 World Gastroenterology Organisation update reach similar conclusions. The American Academy of Pediatrics has not endorsed routine use but does not advise against it.

What it does not solve

The probiotic does not "cure" colic — even in the positive trials, the natural history of colic (peaking around 6 weeks, largely resolved by 3–4 months) accounts for much of the change. L. reuteri reduces crying time, often modestly. It does not address feeding difficulties, reflux, cow's milk protein allergy, or maternal mental health issues that frequently accompany the colic presentation [5]. Anyone treating colic should consider these differential diagnoses, particularly if symptoms include vomiting, poor weight gain, or blood in stool.

Safety in newborns

The safety record for L. reuteri DSM 17938 in immunocompetent term infants is excellent. The strain has been used in pre-term infants for sepsis and necrotising enterocolitis prevention without notable adverse events [6]. The standard contraindications for probiotics in newborns — severe immunodeficiency, central venous catheters, severe critical illness — apply. The product is a sunflower-oil suspension of live bacteria delivered with a metered dropper; storage in the refrigerator extends shelf life.

How to use it in practice

The dose used in trials is 5 drops (10⁸ CFU) given orally once daily, usually in the morning, before breastfeeding or with a small amount of expressed milk. Start within the first 3 weeks of life if colic is established. Trial protocols typically continue for 21–28 days. Effects, when they occur, are usually noticeable within 1–2 weeks. If no improvement after 4 weeks of consistent dosing, the strain is unlikely to be the right intervention for that infant.

Practical takeaway

For an exclusively breastfed infant with classic colic, L. reuteri DSM 17938 at the trial dose for 3–4 weeks is a reasonable, low-risk option with the strongest evidence of any current intervention. It is not transformative, it is not a treatment for the root cause (which remains unclear), and it is most useful as part of a broader plan that includes feeding assessment, parental support, and reassurance about the natural history. Formula-fed infants have less evidence supporting probiotic use for colic.