Background: Otilonium bromide (OB) is a spasmolytic agent acting as an L-type calcium channel antagonist in intestinal and colonic smooth muscle cells (SMCs). We analyzed three independent clinical trials with homogeneous design on patients with irritable bowel syndrome (IBS). After 2 weeks receiving placebo, patients were randomized to receive OB (3 x 40 mg daily) or placebo for 15 weeks. We aimed to perform a pooled analysis of the data from these homogeneous clinical trials to evaluate the efficacy of OB treatment on symptoms and global response of patients. Methods: A total of 883 patients with IBS (69.8% women, mean age 46.2 years, 43.8% mixed type) were included, 442 treated with OB and 441 with placebo. The efficacy results from the three studies at weeks 5, 10 and 15 were pooled in an intention-to-treat (ITT) strategy, analyzed with a logistic regression model and described by forest plots. Results: Despite a placebo effect in all efficacy variables, a significant therapeutic effect of OB was observed at weeks 10 and 15 with reference to: (a) intensity and frequency of abdominal pain; (b) rate of responders as evaluated by patients (71.8% at week 10 and 77.2% at week 15); (c) severity of bloating; (d) rate of responders as evaluated by physicians (55% at week 10 and 63.9% at week 15). No significant OB effect was observed in stool frequency and consistency. Conclusions: OB is more effective than placebo in IBS treatment. Therapeutic benefits are significant after 10 weeks and are maximal after 15 weeks of treatment.