The enthusiasm for probiotics is generally greater than expected based on the data available to support their use for many indications. This has been discussed several times on this blog (see below). The reasons why probiotics are sometimes not effective can be related to being poorly regulated/lack rigorous production standards; even in conditions in which there is some effectiveness (eg. antibiotic-associated diarrhea [AAD]), the number of persons needed to treat for one person to benefit is fairly high. Furthermore, as a recent study (A Olek et al. J Pediatr 2017; 186: 82-6) shows, even in conditions like AAD in which probiotics have proven efficacy, the effects may be strain-specific and/or dose-related.
Olek et al showed that Lactobacillus planatarum DSM9843 (LP299V) was NOT beneficial compared to placebo in reducing the incidence of loose/watery stools or mean number of stools among 438 children receiving outpatient antibiotic therapy.
Specifics: This was a prospective, double-blind, randomized, placebo-controlled parallel-group study. The treatment group received LP299V during antibiotic therapy and for 1 week afterwards. In addition to monitoring the number of stools, the authors determined the frequency of AAD which they defined according to WHO guidelines (>3 loose/watery stools/24 hours after initiation of antibiotics). In this study, AAD was confined to study duration rather than over 2 months.
- Overall, 44.5% of children developed loose/watery stools among placebo group and 39% among probiotic group
- 4.1% developed AAD among placebo group and 2.8% among LP299V
- LP299V showed no significant beneficial effects in reducing AAD or loose/watery stools
The authors note that LP299V has been effective in studies involving adult hospitalized patients. They question whether healthy children, therefore, may be less likely to benefit from probiotics and whether a higher dose could have been more effective.
My take: “Data from clinical studies on probiotics are conflicting” for many conditions, including antibiotic-associated diarrhea.
Related blog posts:
- Balanced summary of probiotics & Microbiome effects on brain
- Probiotics for Crohn’s Disease –No Beneficial Effects Noted | gutsandgrowth
- Probiotics For Fatty Liver Disease | gutsandgrowth
- “Low quality of evidence; strong recommendation” for Probiotics in Gastroenteritis
- Probiotics for Colic
- Do Probiotics Really Help Crying Infants? | gutsandgrowth
- Pushback on Probiotics
- One More Day Syndrome & Necrotizing Enterocolitis | gutsandgrowth
- Probiotics, Atopy, and Asthma | gutsandgrowth

Side note….many probiotics are now offered in a “kids” friendly option, either powder packet or chewable with flavors. Unfortunately, the sweetener/flavoring often has potential to worsen diarrhea. The dosing is usually the same as adult version but the cost is often increased!
Yup, and purchasing decisions are fraught — the labels and names and “doses” (colony counts) are confusing. I’m not entirely confident that what’s on the label is necessarily in the bottle, either (based on studies of other unregulated supplements.) It’s like the Wild West out there.