https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4034083/
>Cannabinoid intoxication can provoke toxic psychoses or symptoms similar to the positive symptoms of schizophrenia
>cannabis seems to provoke an amotivational syndrome similar to the negative symptoms of schizophrenia
>In humans, mounting evidence shows that CB1 receptor densities are altered in schizophrenia

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3138655/
>Our finding of increased CB1R binding in paranoid SCZ could reflect a greater involvement of the endocannabinoid system in the DLPFC in this subtype of patients with SCZ as may be suggested by their more marked positive thought disorders and delusional symptoms.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4104335/
>We provide evidence that regular cannabis use is associated with gray matter volume reduction in the medial temporal cortex, temporal pole, parahippocampal gyrus, insula, and orbitofrontal cortex; these regions are rich in cannabinoid CB1 receptors and functionally associated with motivational, emotional, and affective processing.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2424288/
>The strongest evidence that cannabis use is a contributory cause of schizophrenia comes from longitudinal studies of large representative samples of the population who have been followed over time to see if cannabis users are at higher risk of developing schizophrenia.
>15-year prospective investigation of cannabis use and schizophrenia in 50,465 Swedish conscripts. The study found that those who had tried cannabis by age 18 were 2.4 times more likely to be diagnosed with schizophrenia than those who had not 16 and the risk of this diagnosis increased with the frequency of cannabis use.
>27-year follow-up of the Swedish cohort that also found a dose-response relationship between frequency of cannabis use at baseline and risk of schizophrenia during the follow-up. The relationship between cannabis use and schizophrenia persisted when the authors statistically controlled for the effects of other drug use and other potential confounding factors, including a history of psychiatric symptoms at baseline.
>supported in a three-year longitudinal study of the relationship between self-reported cannabis use and psychosis in a community sample of 4,848 people in the Netherlands
>These findings have been replicated in one German and two New Zealand cohort studies.

https://www.drugabuse.gov/news-events/nida-notes/2016/09/regular-marijuana-use-associated-differences-in-brain-gray-matter-connectivity
>A NIDA-funded brain imaging study has shown that regular users of marijuana have less gray matter than nonusers of the drug in the orbitofrontal cortex (OFC), a brain region that contributes to impulse control, decision-making, and learning. Such a deficit could make it more difficult to change counterproductive behaviors, including drug use.