Comorbidity with anxiety and substance use disorders in patients with schizophrenia

Objective Anxiety disorders and alcohol/substance use disorders (SUD) are very common in schizophrenia (SCH). Studies investigating the relationship between SUD and anxiety in patients with SCH are scanty, and virtually absent in the Mediterranean area. The aim of the present study is to analyse the relationship between anxiety disorders and SUD in patients with SCH. We hypothesized that comorbidity with anxiety disorders would be more frequent in patients with SCH and SUD compared with those without SUD. Methods Participants were recruited in the framework of two research programs coordinated by the Department of Psychiatry, Neurobiology, Pharmacology and Biotechnologies (DPNFB) of the University of Pisa, Italy aimed to investigate the comorbidity of patients with severe mental illness using standardized interviews. The first research program was carried out between September 2003 and March 2005 at nine Departments of Mental Health located in Tuscany, the second program included consecutive patients with schizophrenia or affective psychoses recruited from the inpatient, day-hospital and outpatient units of the Psychiatric Clinic of the DPNFB between April 2003 and March 2006. Eligible subjects were inpatients and outpatients with chronic psychotic disorders between the ages of 18-65 years in treatment for at least one year. The diagnostic assessment was carried-out using the Structured Clinical Interview for DSM-IV Axis-I Disorders (SCID-I). Comparisons of categorical variables between groups were carried out using the chi-square test or Fisher's exact test when appropriate. Analyses were carried out first separately in the two study groups. Logistic regression was then used to analyse in the pooled sample the association between anxiety disorders and SUD, adjusted for gender, age, and study. Results Participants included 145 patients with SCH in study 1 and 30 in study 2 (Table I). The lifetime prevalence of SUD was 18.6% vs. 50% (chi-square = 13.42, p < 0.01). The lifetime prevalence of anxiety disorders was 32.4% in study 1 and 43.3% in study 2 (chi-square = 1.31, p = 0.251). In both study 1 and study 2, lifetime SUD was associated with significantly greater odds of anxiety disorders (OR = 2.8, 95% CI 1.2-6.5; OR = 8.0, 95% CI 1.5-42.0) (Table III). Logistic regression analysis carried out on the pooled sample indicated that this association continued to be significant (OR = 3.8, 95% CI 1.8-8.4, p < 0.001) after controlling age, gender, and study. Conclusion We found a significant association between SUD and anxiety disorders in patients with SCH. In these patients, substance use could be an attempt to reduce anxiety symptoms and to improve social performance. Further studies with a longitudinal design are warranted to elucidate the reciprocal causal mechanisms underlying the comorbidity between SCH with SUD and anxiety disorders. In addition, it will be important to determine whether effective treatment of anxiety symptoms can improve treatment response in schizophrenia and SUD.