Significant psychological morbidity occurs in irritable bowel syndrome: a case-control study using a pharmacy reimbursement database.

Background: Psychological problems are associated with IBS but the strength of this association is unclear.

Aim: To assess co-prescribing of antispasmodic and CNS-acting drugs through a nested case-control study.

Methods: A national dispensing database identified patients who were first dispensed antispasmodic medicines for a continuous 3-month period or more during 2006, using 2005 as a run-in period. Each patient was matched with four control patients and excluded if they received drugs indicated for IBD.

Results: Four hundred and seven patients commenced antispasmodic drugs during 2006. These patients were matched with 1628 controls. In 2005, patients subsequently prescribed antispasmodics were 2-3 times more likely to receive CNS-acting drugs than controls. In the year following commencement of IBS therapy, patients were 2-4 times more likely than controls to be prescribed CNS-acting drugs including antidepressants (35.4% vs. 9.3%), anxiolytics (27.8% vs. 8.8%), antipsychotics (9.8% vs. 3.3%) and hypno-sedatives (32.7% vs. 11.3%; P < 0.0001). The adjusted OR (95% CI) for antidepressant, anxiolytic, hypnosedative and antipsychotic prescribing in IBS patients were 3.81 (2.79-5.20), 2.84 (2.12-3.81), 2.62 (1.91-3.60) and 2.58 (1.80-3.66), respectively.

Conclusions: Patients prescribed ongoing therapy for presumed IBS are 2-4 times more likely to be prescribed CNS-acting drugs than controls, providing evidence of psychological comorbidity in IBS.