A common-factor as an explanation for the association between schizotypy and cannabis use

There is a robust association between cannabis use and increased risk for schizophrenia. This relationship generalises to schizotypy, a schizophrenia-liability state. Cannabis use seems to be associated with increased positive (or cognitive-perceptual) and decreased negative symptomatology. The aim of the present study was to examine the longitudinal association of cannabis use with features of schizotypy to test whether this relationship may be due to schizotypal vulnerability, self-medicating behaviour, or common risk factors. In Phase 1, undergraduate psychology students (n = 1462) completed the Schizotypal Personality Questionnaire (SPQ), the Kanner Hassles Scale (KHS), and gave information on cannabis use behaviours. Taxometric methods were used to classify participants as schizotypal or not schizotypal. In Phase 2, schizotypal and non-schizotypal participants from Phase 1 were invited to complete a follow-up assessment 6 to 10 years later. Of n = 259 who were invited to complete Phase 2, n = 85 did so, providing responses on the SPQ, Acute Hassles Scale (AHS), and cannabis use behaviour questionnaires. Baseline schizotypy group membership did not interact with cannabis use to predict positive features of schizotypy at follow up. Baseline interpersonal features of schizotypy did not predict cannabis use behaviours. In the absence of baseline cannabis use, baseline positive features of schizotypy predicted lifetime cannabis use among the baseline schizotypy group, and current cannabis use among the whole sample. The pattern of results suggests that a common risk factor underlying cannabis use behaviours and schizotypy may explain different aspects of the association between positive features of schizotypy and cannabis use behaviours. That is, positive features may precede cannabis use