CRD Summary: The authors concluded that probiotics may improve symptoms in patients with irritable bowel syndrome, but that benefits were uncertain and further research was required. The authors’ cautious conclusion appeared to reflect the evidence presented, but the limited search, lack of reporting of review methods and an incomplete validity assessment made it difficult to comment on reliability.

CRD Commentary: The review question was clearly stated. Inclusion criteria were defined for study design, intervention and control and participants. Limiting the search to studies identified in one database plus references may have missed other relevant studies and risked publication bias. It was not clear if attempts were made to minimise language bias. Methods used to select studies and extract data were not described, so it was not known whether efforts were made to reduce reviewer errors and bias. Only studies that used some level of blinding were eligible, but no other aspect of study validity was assessed and so results from these studies and any synthesis may not be reliable. In view of the diversity among studies, a narrative synthesis was appropriate. The authors’ cautious conclusion appeared to reflect the evidence presented, but the limited search, lack of reporting of review methods and the incomplete validity assessment made it difficult to comment on reliability.