Background  Dextofisopam modulates stimulated activity in animal models of stress, altered bowel motility, and visceral hypersensitivity.

Aim  To evaluate the effects of dextofisopam in men and women with diarrhoea‐predominant or alternating irritable bowel syndrome (IBS) (d‐IBS or a‐IBS).

Methods  In this double‐blind, placebo‐controlled study, patients were randomly assigned to receive dextofisopam 200 mg b.d. or placebo for 12 weeks. The prospectively defined primary endpoint was number of months of adequate overall relief of IBS symptoms. Bowel function was assessed primarily via stool frequency and consistency.

Results  Of 140 enrolled patients, 66 received dextofisopam and 74 placebo; 73% of the patients were women, and 78% had d‐IBS. Dextofisopam was superior to placebo on the primary endpoint (P = 0.033). In d‐IBS patients treated with dextofisopam, both men and women had improved stool consistency, but stool frequency was reduced only in women. Benefit diminished over time on the primary endpoint, but persisted on frequency and consistency. Dextofisopam and placebo had similar rates and types of adverse events, with more events of worsening abdominal pain with dextofisopam (12% vs. 4%) and more headaches with placebo (12% vs. 5%). Constipation was rare.

Conclusion  Dextofisopam should be further evaluated as a new treatment for men and women with d‐IBS and a‐IBS.