Substance use and schizophrenia: Adverse correlates in the CATIE study sample

Objective: This study examined the relationship between severity of illicit substance use at the time of study entry in a sample of patients diagnosed with schizophrenia and 18-month longitudinal outcomes, including psychopathology, depression, neurocognition, and quality of life. Methods: Subjects in the Clinical Antipsychotic Trials of Intervention Effectiveness (N = 1432) were divided into three groups according to baseline data: (1) those with moderate/severe drug use, (2) those with mild drug use, and (3) non-users of illicit substances. The groups were compared on other baseline characteristics. Mixed model analysis was used to compare outcomes between the groups using all available outcome data over 18. months, controlling for potential confounding baseline characteristics. Least square means were compared between pairs of groups in the mixed models. Results: Significantly poorer outcomes were observed in the domains of psychosis, symptoms of depression, and quality of life for moderate/severe drug users in comparison with both mild users and abstainers. No significant differences were found on neurocognitive functioning or days of employment. Conclusions: This study suggests that drug use-related impairment co-morbid with schizophrenia may not be a function of use per se but rather, of the severity of use. It highlights the importance of comprehensive assessment and treatment of illicit substance abuse in schizophrenia. Long-term treatment approaches that integrate harm reduction strategies may offer promise in maximizing positive outcomes for such dually diagnosed patients.