>>9529429>Does something in american society cause schizophrenia?Regular cannabis use and psychotic disorders (such as schizophrenia) are associated in the general population 1,2, and heavy cannabis users are over-represented among new cases of schizophrenia 3-5,. These findings, and rising rates of cannabis use among young people in many developed countries, have prompted debates about whether cannabis use may be a contributory cause of psychosis, that is, it may precipitate schizophrenia in vulnerable individuals. This hypothesis assumes that cannabis use is one factor among many others (including genetic predisposition and other unknown causes) that together cause schizophrenia.
There are also other possible explanations of the association. Common factors may increase the risk of cannabis use and psychosis, without the two being directly related. Cannabis could also be used to self-medicate the symptoms of schizophrenia 6-15.
The consistent finding of an association between cannabis use and psychosis makes chance an unlikely explanation of the association, and there are also now a number of prospective studies showing that cannabis use often precedes psychosis. The more difficult task has been excluding the hypothesis that the relationship is due to other factors, such as other drug use or a genetic predisposition to develop schizophrenia and use cannabis.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2424288/ 
