Patterns in adolescent cannabis use predict the onset and symptom structure of schizophrenia-spectrum disorder

This study investigated adolescent cannabis use as a risk factor for schizophrenia spectrum disorder (SSD). Motives for early cannabis use and resulting usage patterns were examined alongside clinical measures of SSD onset and symptomatology. Participants (N = 178) were recruited for two samples, 1: healthy controls (HC) with cannabis use, 2: schizophrenia patients (SSD) with cannabis use. Structured interviews of participants and family informants were used to obtain diagnostic and biographical information. Factor-analysis of reported motives for initiating cannabis use produced four groups; sedation, stimulation, social pressure, and recreation. Regression analyses revealed significant relationships between these groups and SSD. Most notably, reason group factor scores predict SSD risk as well as schizotypal symptom severity. Findings also indicate that these factors follow a hierarchical structure, which explains their relative involvement in increased SSD risk. We suggest that adolescent cannabis use both hastens the onset and amplifies the severity of SSD. In response we propose a model for identifying at risk individuals, predicting the onset and severity of SSD, and potentially mitigating the associated psychiatric impairments.