This Editorial analyzes the paper by Schnadower et al on the secondary analysis of 2 randomized placebo-controlled trials evaluating the efficacy of Lactobacillus rhamnosus GG, and a combination of L. rhamnosus R0011 and L. helveticus R0052, showing that moderate-to-severe gastroenteritis symptoms as primary endpoint, did not differ between probiotics or placebo. The data is important because probiotics are commonly used and prescribed in clinical practice, many times without strong evidence and producing a high economic burden. Two other examples are addressed. A systematic review of randomized placebo-controlled trial of L. reuteri DSM 17938 finding that this probiotic reduced the duration of diarrhea and hospitalization, to discuss the issue that the effect of probiotics is strain specific. In addition, the different findings of reviews and meta-analyses of probiotics in Irritable Bowel Syndrome in which a common conclusion of all of them was that adequately powered randomized controlled trials are required to better determine the species, strains and doses of probiotics, as well as the treatment duration that is most efficacious. Finally, the fact that probiotics are frequently prescribed despite lacking regulations by pharmaceutical authorities is addressed.