The lifetime and past-year prevalence of dual diagnosis in people with schizophrenia across Europe: findings from the European Schizophrenia Cohort (EuroSC)

Relatively little is known about rates of comorbid drug and alcohol problems in people with schizophrenia outside the USA. Most studies have recruited from single countries. Newly available data provided an unmatched opportunity to investigate the prevalence of comorbid dependence on alcohol and other psychoactive substances in people with schizophrenia in France, Germany and the UK at the same time. The European Schizophrenia Cohort study data set used semi-structured clinical interviews to establish DSM-IV diagnoses. 1,208 patients were interviewed in nine centres. The lifetime rate for comorbid dependence on any substance was highest in the UK (35 %), but considerably lower in Germany (21 %) and in France (19 %), and generally more than double the past-year rates. Dependence on alcohol and on other psychoactive substances showed similar variations (comorbid alcohol dependence: UK 26 %; Germany 18 %; France 14 %; comorbid drug dependence: UK 18 %; Germany 8 %; France 7 %). Differences within countries persisted after controlling for individual characteristics. The relative odds of dependence were higher than in the general population, but varied between countries and centres. Dependence disorders are a common problem in people with schizophrenia in Western Europe, although effective service configurations have yet to be developed. Overall, these European rates are less than those reported from the USA. Research comparing people with current comorbidity with those who are no longer dependent is needed.