Heavy marijuana (MJ) use in adolescence has been associated with 2-4 fold increased risk for schizophrenia (SZ) in later life. It is unclear if lighter and more sporadic MJ exposure (i.e. recreational MJ use), a pattern more typical of most adolescent users, has similar deleterious effects especially when more potent forms of MJ have become the norm during the past 2 decades. In a recently completed 3-year longitudinal study, we found that unaffected adolescent first-degree biological relatives of schizophrenia patients with recreational MJ use failed to show age-expected maturation in processing speed and executive functioning and in pruning of gray matter cortical thickness within dorsolateral prefrontal and parieto-temporal brain regions. The overall objective of this ALSPAC proposal are to understand the nature of the association between adolescent recreational MJ use and schizophrenia susceptibility. The specific aims are to delineate the impact of adolescent recreational MJ use on cognitive maturation, brain cortical development and its specificity on risks for developing schizophrenia and other common psychiatric disorders in later life.