A substantial body of published research over the past 40 years has established that functional gastrointestinal disorders have an unusually large overlap with several non-gastrointestinal pain syndromes, including fibromyalgia, chronic pelvic pain, and temporomandibular joint disorder. Migraine has also been found to have such excess comorbidity with functional gastrointestinal disorders. For example, a meta-analysis of six studies reported an overall odds ratio (OR) of 2·66 for migraine in individuals with irritable bowel syndrome (IBS)
