A systematic review revealed the inadequacy of adverse event data in clinical trials of probiotics and prebiotics, rendering it difficult to draw broad conclusions with regards to the safety of interventions to modify gut micro-organisms. These randomized trials assessed probiotics, prebiotics, or synbiotics, which are products that combine probiotics and probiotics.

The authors of the review which was published in the  Annals of Internal Medicine, led by Aïda Bafeta, PhD, Centre d’Épidémiologie Clinique, Hôpital Hôtel-Dieu, Paris, pointed out that about a third of 384 randomized clinical trials shared no data on potential harms associated with probiotics, prebiotics, or products that combine the two. Only 2% of the trials reported the necessary key safety components.

 “The inadequacy in reporting harms-related results may lead to an inaccurate safety profile and erroneous decision making, with major consequences for patients,” Dr. Bafeta and her colleagues wrote in their review.

Thorough safety evaluations may be deemed unnecessary by some, but caution is particularly essential when considering the use of probiotics and prebiotics in critically ill patients, as per the authors. They also wrote, “More worrying is that potential risks have been described in case reports and clinical trial results.”

Dr. Bafeta along with her co-authors cited a randomized, placebo-controlled trial published in The Lancet in 2008, showing an augmented risk of mortality after prophylactic administration of a particular combination of probiotic strains in patients having risk of severe acute pancreatitis.

The Agency for Healthcare Research and Quality submitted a report in 2011 which stated that existing literature at that time was “not well equipped” to confidently comment on the safety of probiotics as administered in clinical trials.