Project 465649

Cannabis is one of the most widely used psychoactive drugs in Canada. Although it is considered a relatively safe substance, the associated increased risk of adverse mental health outcomes, including psychosis, presents a significant public health concern. Cannabis use, especially heavy use at early ages (15-16 years) is linked with increased frequency of psychosis symptoms and risk of developing a psychotic disorder such as schizophrenia. The brain mechanisms of the cannabis-psychosis relationship remain poorly understood. The aim of this project is to improve our understanding of the links between cannabis, psychosis and brain structure and function. We will pursue these aims by: (1) adding a detailed assessments of psychosis, cannabis use/dependence and neurocognition to a ten-year population-based longitudinal cohort of 3800 youth; and (2) adding a novel PET-neuroimaging protocol to a subsample (n=48) of this longitudinal cohort for whom repeated neuroimaging data are available. We aim to measure connections between neurons (synaptic density) using a highly novel neuroimaging method in early-onset cannabis users (started at 16 years or younger) and individuals who did not use cannabis during adolescence. We hypothesize that early-onset cannabis users will exhibit poorer neurocognitive outcomes and lower synaptic density in brain regions related to cognitive functioning compared to non users or late-onset users. Reduced synaptic density in these regions will be associated with psychosis symptoms and impaired cognitive performance.