Search Strategy and Selection Criteria

We included all eligible randomized placebo-controlled, trials (RCTs) of probiotics treatment in adult IBS. We searched Medline(1966 to Jan 2019), Embase(1974 to Jan 2019), the Cochrane Central Register of Controlled Trials(up to Jan 2019), the ClinicalTrials.gov trials register(up to Jan 2019), and Chinese Biomedical Literature Database(CBM) (1978 to Jan 2019) for relevant trials. We used the terms “probiotics” and “irritable bowel syndrome” both as medical subject heading (Mesh) and free text terms. The exact search strategy in Medline was (“probiotics”[MeSH Terms] OR “probiotics”[Title/Abstract]) AND (“irritable bowel syndrome”[MeSH Terms] OR “irritable bowel syndrome”[Title/Abstract]) AND (“randomized controlled trial” [pt] OR “randomized controlled trial” [tiab]).

We used the following eligibility criteria: (1) the studies were randomized controlled trials (RCTs) comparing probiotics with placebo; (2) diagnostic criteria included but were not limited to the Manning criteria, and Rome I, Rome II, or Rome III criteria. We did not exclude trials in which patients were stated to be diagnosed with IBS but no diagnostic criteria were described; (3) the age of participants were ≥ 18 years; (4) minimum treatment duration was 7 days. Studies were excluded if they met: (1) studies with inadequate information; (2) probiotics along with other drugs; (3) control group was not placebo; (4) data were not available after contacting the authors. There were no language limitation. Articles in foreign language were translated as needed.