Irritable bowel syndrome (IBS) occurs more frequently in psychiatric patients, especially those with anxiety and mood disorders.

We sought to determine the prevalence and phenomenology of IBS in patients diagnosed with obsessive-compulsive disorder (OCD). A semi-structured diagnostic interview was administered to patients seeking treatment for OCD in outpatient settings. Structured questions regarding gastrointestinal functioning and IBS symptoms were administered. IBS was diagnosed by a gastroenterologist using Rome I criteria.

Thirty-seven patients (35.1%) with OCD met criteria for IBS. Of these, 53.8% had IBS with both diarrhea and constipation, 30.8% had diarrhea-predominant IBS, and 15.4% had constipation-predominant IBS.The prevalence rate of IBS in an age- and sex-matched control group (n=40) of medical patients in a family practice was 2.5%. IBS prevalence rates were significantly higher for OCD patients than control subjects (P=.0002).

IBS and psychiatric illness have high rates of bi-directional comorbidity. This study shows that 35.1% of patients with OCD satisfied criteria for IBS in contrast to 2.5% of the controlled subjects. In most patients the IBS was characterized by both diarrhea and constipation. While taking the initial history clinicians should inquire about bowel symptoms in patients presenting with psychiatric illnesses, including OCD. SSRIs could potentially worsen such symptoms and lead to non-adherence.