Irritable bowel syndrome is a common condition with a community prevalence of 10-15% of the general population.1 2 The annual incidence in primary care is around 0.8%, and the prevalence of patients diagnosed in primary care is about 3-4%.3 The disorder is difficult to treat, hence the wide range of treatments used—dietary exclusion, fibre supplements, and probiotics; antispasmodic drugs, antidiarrhoeal agents, and laxatives; antidepressants, hypnotherapy, and cognitive behavioural therapy. This unusual spectrum of drug and non-drug treatments also highlights our ignorance about the cause of the condition. In the linked systematic review (doi:10.1136/bmj.a2313), Ford and colleagues summarise the effects of three different agents—fibre, antispasmodic drugs, and peppermint oil—in people with the syndrome.4

In the 1990s a range of new agents acting on 5-hydroxytryptamine type 3 and type 4 receptors in the enteric nervous system held considerable therapeutic promise. Most of them, however, failed to find a …