Inadequate safety data exist to support the use of probiotic, prebiotic, and synbiotic interventions, according to research published in the Annals of Internal Medicine.

Aïda Bafeta, PhD, from the Centre d’Epidémiologie Clinique at the Hôpital Hôtel-Dieu in Paris, France, and colleagues conducted a systematic review of randomized controlled trials that assessed safety or efficacy of at least 1 probiotic, prebiotic, or synbiotic patient intervention. Trials were gathered from the Cochrane Central Register of Controlled Trials, PubMed, EMBASE, and Web of Science between January 2015 and March 2018.

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Researchers included 384 trials in the systematic review; 136 studies were conducted in healthy volunteers, and 248 were conducted in patients with “any of several medical conditions.” Of those, 339 were published in specialty journals. Probiotics were most commonly examined (69% of studies).

In 28% and 37% of trials, respectively, no harms-related or safety result data were reported. Eighty percent of trials did not include the number of serious adverse events. Results of the systematic review also indicated that in studies that did indicate harms-related results, 37% used “generic statements” to describe adverse events and 16% used “inadequate metrics.” In 98% of trials, no definition for adverse events or serious adverse events was provided.

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The researchers acknowledged that “[s]afety data may be omitted from RCT reports for several reasons. People have strong beliefs about the safety of probiotics, prebiotics, and synbiotics. Many researchers in this area think that a detailed evaluation of potential harms is not necessary.”

They continued: “Caution is needed, however, particularly when considering these interventions for vulnerable or critically ill persons. The safety profile of an intervention should never be presumed.”

Primary study limitations include the possible effect of journal publication processes, and the inclusion of English-language publications only, which limits generalizability of results.


Bafeta A, Koh M, Riveros C, Ravaud P. Harms reporting in randomized controlled trials of interventions aimed at modifying microbiota [published online July 16, 2018]. Ann Intern Med. doi:10.7326/M18-0343