Background: Consistent guidance for choosing an appropriate probiotic for the treatment of irritable bowel syndrome is lacking. Methods: Literature databases searched included: PubMed, Google Scholar and NIH registry of clinical trials from inception to June 2021. Inclusion criteria: randomized controlled trials (RCTs) enrolling adult or pediatric IBS patients comparing probiotics against controls and 2 RCTs with common IBS outcome measures within each type of probiotic. Five common measures of IBS symptoms (changes in global Irritable Bowel Syndrome Severity Scoring System or IBS-SSS scores, frequency of global responders, changes in bloating or abdominal pain scores and frequency of abdominal pain relief) were used. This study was registered at Prospero (#CRD42018109169). Findings: We screened 521 studies and included 42 randomized controlled trials (45 treatment arms, N = 3856). Four probiotics demonstrated significant reduction in abdominal pain relief: B. coagulans MTCC5260 (RR= 4 . 9, 95% C.I. 3 . 3, 7 . 3), L. plantarum 299v (RR= 4 . 6, 95% CI 1 . 9, 11 . 0), S. boulardii CNCM I-745 (RR= 1 . 5, 95% C.I. 1 . 1, 2 . 1) and S. cerevisiae CNCM I-3856 (RR= 1 . 3, 95% C.I. 1 . 04, 1 . 6). Mild-moderate adverse events were reported in 51% of the trials, none were more associated with the probiotic compared to controls. Interpretation: Although the analysis of probiotic efficacy was limited by the diversity of IBS outcomes used in trials and lack of confirmatory trials for some strains, six single-strain probiotics and three different types of probiotic mixtures showed significant efficacy for at least one IBS outcome measure. These results might be relevant to clinical practice and policy.