Psychopathology in dual diagnosis and non-addicted schizophrenics--are there differences?

In a previous publication we reported lifetime and 3-month prevalence estimates for substance use in two large samples of schizophrenic inpatients (Soyka et al. 1993). A subsequent analysis of psychopathological findings assessed by means of the AMDP Manual (Guy and Ban 1982) in schizophrenic in-patients of the Haar Mental State Hospital (N=447), in whom a lifetime prevalence for substance use of 42.9% (3-month prevalence 29%) had been reported, was performed. While the overall differences between substance using (dual diagnosis) and nonusing schizophrenics were small, dual diagnosis patients in general reported more positive symptoms, especially more intense hallucinations. These differences could basically be demonstrated in patients with current (3-month) substance use on admission but not on discharge possibly as a result of substance use. Most marked and highly significant results were found with respect to previous suicide attempts and delinquency which were more prevalent in dual diagnosis schizophrenics. Results of this study indicate that dual diagnosis patients compared to other schizophrenics represent a more disturbed patient group. Implications for the self-medication hypothesis for substance use in schizophrenia and future research in this area are discussed.