Comorbidity of common mental disorders and alcohol or other substance misuse in Australian general practice.

Objective: To determine in patients attending general practice 1) the extent of comorbidity of mental disorders and alcohol or other substance misuse, and consequent disability; and 2) GPs' diagnosis and management of patients with comorbidity.

Design And Setting: Cross-sectional national audit of general practices throughout Australia in 1998-1999.

Participants: 46 515 ambulatory care patients attending 386 GPs.

Screening Tools: Prevalence of common mental disorders--12 items from the 34-item SPHERE self-report questionnaire and associated classification system; prevalence of alcohol or other substance misuse--two self-report screening questions, defining "probable" misuse (a positive response to both questions) and "possible" misuse (a positive response to one of the questions); disability--four items from the Brief Disability Questionnaire, and self-reported "days out of role" and "days in bed" in the past month; and rates of psychological diagnosis, treatment and referral by GPs, and GPs' rating of patients' psychological risk.

Main Outcome Measures: Comorbidity of mental disorders and alcohol or other substance misuse; disability; and correlation with GPs' diagnosis and management.

Results: The screening questions revealed possible alcohol or other substance misuse in 11% of patients (5171/46515), and probable misuse in an additional 8% of patients (3593/46515). Comorbidity of mental disorders and substance misuse occurred in 12% (5672/46515) of patients. Patients with comorbidity (compared with those with alcohol or other substance misuse alone) were: more disabled--mean "days out of role in the last month", 8.4 (95% CI, 7.7-9.1) v 3.6 (95% CI, 2.9-4.3); at greater psychological risk (as rated by GPs)--22% v 7%, respectively; more frequently given psychological diagnoses by GPs--51% v 21%; more frequently treated for a psychological condition by GPs--47% v 17%; and more frequently referred to mental health specialists by GPs--9% v 2%.

Conclusion: Comorbidity of mental disorders and alcohol or other substance misuse is common in patients attending general practice, and results in considerable disability. Such patients receive inadequate attention (diagnosis and management) from GPs. GPs identifying one of these two types of behaviour disorder in a patient should ascertain whether the other type is also present.