Considering that jurisdictions are moving toward cannabis legalization and the anticipated changes to the Canadian policy planned for July 2018, there is a need to understand whether cannabis use has a causal role in the development of psychiatric diseases, such as psychosis. Prospective studies report a temporal precedence of cannabis use before later onset of psychosis, but the evidence is limited with respect to causality due to studies only assessing psychosis symptoms (PS) at a single follow-up and by relying on analytic models that might confound intra-individual processes with initial between-person differences. In the absence of an experimental design, random intercept cross-lagged panel models (RI-CLPMs) provide the most rigorous test of causal predominance between 2 outcomes by quantifying the temporal association over multiple follow-up periods and by dissociating within-person and between-person variance. Using this approach, we investigated year-to-year associations between cannabis use and PS over 4 years in youth aged 13 years at study onset.
Josiane Bourque, MSc; Mohammad H. Afzali, PhD; Patricia J. Conrod, PhD
JAMA Psychiatry. 2018;75(8)