Introduction: Probiotics may benefit irritable bowel syndrome (IBS) symptoms but randomized controlled trials (RCTs) have been conflicting so we conducted a systematic review.
Methods: MEDLINE, EMBASE, and the Cochrane Controlled Trials Register electronic databases were searched (up to May 2008), as were conference proceedings, and authors were contacted for extra information. We included only parallel group RCTs with at least one week of therapy comparing probiotics with placebo or no treatment in adults with IBS according to any acceptable definition. Studies had to provide abdominal pain or global IBS symptom improvement as an outcome. Eligibility assessment and data extraction were performed by two independent researchers. Data were synthesized using relative risk (RR) of symptoms persisting for dichotomous data and standardized mean difference (SMD) for continuous data using random effects models.
Results: We identified 19 RCTs. Trial quality was generally good. There were 10 RCTs involving 918 patients providing dichotomous data. Probiotics were statistically significantly better than placebo (RR of IBS not improving = 0.71; 95% CI 0.57-0.88) with an NNT = 4 (95% CI = 3-12.5). There was significant heterogeneity (I2 = 68%) and possible funnel plot asymmetry. Fifteen trials assessing 1351 patients reported on improvement in IBS score as a continuous outcome (SMD = -0.34; 95% CI -0.60 to -0.07). There was statistically significant heterogeneity (I2 = 79%), but this was explained by one outlying trial.
Conclusion: Probiotics appear to be efficacious in IBS but the magnitude of benefit and the most effective species and strain are uncertain.