Objective: Despite evidence demonstrating elevated comorbidity between schizophrenia and substance use disorders, the underlying mechanisms of association remain poorly understood. The brief time intervals that characterize interactions between substance use and psychotic symptoms in daily life are inaccessible to standard research protocols. The authors used electronic personal digital assistants (PDAs) to examine the temporal association of diverse forms of substance use with psychotic symptoms and psychological states in natural contexts.
Method: Of 199 community-dwelling individuals with schizophrenia or schizoaffective disorder who were contacted to participate in the study, 92% accepted and 73% completed the study. The 145 participants who completed the study provided reports of substance use, psychotic symptoms, mood, and event negativity multiple times per day over 7 consecutive days through PDAs.
Results: Participants responded to 72% of the electronic interviews (N=2,737) across daily life contexts. Strong within-day prospective associations were observed in both directions between substance use and negative psychological states or psychotic symptoms, but considerable variation was observed by substance type. Consistent with the notion of self-medication, alcohol use was most likely to follow increases in anxious mood or psychotic symptoms. Cannabis and other illicit substances, demonstrating more complex patterns, were more likely to follow certain psychological states but were also associated with the later onset of psychotic symptoms.
Conclusions: The dynamic interplay of substance use and psychotic symptoms is in many cases consistent with both causal and self-medication mechanisms, and these patterns of association should be considered in the design of treatment and prevention strategies.