http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2424288/
"Regular cannabis use predicts an increased risk of schizophrenia, and the relationship persists after controlling for confounding variables. The relationship is unlikely to be explained by self-medication. There is increasing evidence that the association is biologically plausible, but given the complex nature of the aetiology of schizophrenia and related disorders, it is unlikely that the relationship will be due to an interaction between cannabis use and a single gene. Uncertainty about the biological mechanisms should not distract us from using educational, psychological and social interventions to reduce the use of cannabis by vulnerable young people and thereby the risk of problems related to its use. "
http://www.ncbi.nlm.nih.gov/pubmed/24904437
"... Exposure to cannabinoids in adolescence confers a higher risk for psychosis outcomes in later life and the risk is dose-related. Individuals with polymorphisms of COMT and AKT1 genes may be at increased risk for psychotic disorders in association with cannabinoids, as are individuals with a family history of psychotic disorders or a history of childhood trauma. The relationship between cannabis and schizophrenia fulfills many but not all of the standard criteria for causality, including temporality, biological gradient, biological plausibility, experimental evidence, consistency, and coherence. At the present time, the evidence indicates that cannabis may be a component cause in the emergence of psychosis, and this warrants serious consideration from the point of view of public health policy. "
http://www.northwestern.edu/newscen...ve-abnormal-brain-structure--poor-memory.html
"Marijuana Users Have Abnormal Brain Structure and Poor Memory
Drug abuse appears to foster brain changes that resemble schizophrenia"
etc etc