From Time.com:
Since the days of Reefer Madness, scientists have sought to understand the complex connection between marijuana and psychosis. Cannabis can cause short-term psychotic experiences, such as hallucinations and paranoia, even in healthy people, but researchers have also long noted a link between marijuana use and the chronic psychotic disorder, schizophrenia.
Repeatedly, studies have found that people with schizophrenia are about twice as likely to smoke pot as those who are unaffected. Conversely, data suggest that those who smoke cannabis are twice as likely to develop schizophrenia as nonsmokers. One widely publicized 2007 review of the research even concluded that trying marijuana just once was associated with a 40% increase in risk of schizophrenia and other psychotic disorders.
