Background: High rates of comorbid alcohol and drug disorders have previously been found among individuals with severe mental illnesses such as schizophrenia and bipolar affective disorders. Clinical and social outcomes have been reported to be worse in this group and service costs greater than in individuals with severe mental illness only. These 'dual diagnosis' patients have mainly been investigated in the USA, and there has been very little research in Europe, where patterns of substance abuse may be different.
Method: All patients with psychotic illnesses who had any contact with the mental health services in a geographically defined sector in South London over a specified period were studied. Individuals with problems related to alcohol or drugs were identified using standardised interviews with subjects and their keyworkers. Data on psychiatric service use during the previous 2 years were also obtained.
Results: One hundred and seventy-one subjects with psychotic illnesses were interviewed (response rate: 78.4%). The one-year prevalence rate for any substance problem was 36.3% (95% CI = 29.1-43.5), for alcohol problems it was 31.6% (95% CI = 24.6-38.5), and for drug problems 15.8% (95% CI = 10.3-21.3). Young male subjects were at higher risk of having substance problems. Patients with substance problems had spent almost twice as many days in hospital as those without such problems over the previous two years (difference = 26.3 days, 95% CI = 3.8-48.7).
Conclusions: The prevalence of substance problems among people suffering from severe mental disorders is high, and seems to be associated with greater use of in-patient services. This is a significant clinical problem, with cost implications. Further investigation is needed for adequate service provision.