Psychosocial functioning, quality of life and clinical correlates of comorbid alcohol and drug dependence syndromes in people with schizophrenia across Europe

Little is known about the correlates of comorbid drug and alcohol dependence in people with schizophrenia outside the USA. We tested hypotheses that dependence on alcohol/drugs would be associated with more severe symptoms, and poorer psychosocial functioning and quality of life. The EuroSC Cohort study (N=1204), based in France, Germany and the UK, used semi-structured clinical interviews for diagnoses, and standardized tools to assess correlates. We used mixed models to compare outcomes between past-year comorbid dependence on alcohol/drugs, controlling for covariates and modelling both subject and country-level effects. Participants dependent on alcohol or drugs had fewer negative symptoms on PANSS than their non-dependent counterparts. However, those dependent on alcohol scored higher on PANSS general psychopathology than those who were not, or dependent only on drugs. People with schizophrenia dependent on drugs had poorer quality of life, more extrapyramidal side effects, and scored worse on Global Assessment of Functioning (GAF) than those without dependence. People with alcohol dependence reported more reasons for non-compliance with medication, and poorer functioning on GAF, though not on Global Assessment of Relational Functioning. In people with schizophrenia, comorbid dependence on alcohol or drugs is associated with impaired clinical and psychosocial adjustment, and poorer quality of life.