Do probiotics shorten diarrhea from an infection?

Large, well-run trials do not show it. A 2020 Cochrane review included 82 studies with 12,127 people, most of them children. In the trials with a low risk of bias, probiotics probably made little or no difference to diarrhea that lasted 48 hours or longer (risk ratio 1.00). The effect on its length was uncertain.^[1] When all the trials were pooled, diarrhea that lasted 48 hours or longer was 36% less common and diarrhea was 21.3 hours shorter, but the results varied widely between trials.^[2][1] No serious side effects were linked to probiotics.^[1]

Expert groups disagree. A European pediatric society gives a weak recommendation for a few named strains, based on low or very low certainty evidence. The American Gastroenterological Association recommends against probiotics for children with this illness in the US and Canada.^[2]