Smoking marijuana as a teenager could raise the risk of developing schizophrenia and psychotic symptoms as a young adult, according to a new study that compared the prevalence of mental illness among marijuana users and non-users.
Bloomberg News reported March 2 that researcher John McGrath of the University of Queensland, Australia, and colleagues studied 3,801 young-adult sibling pairs and concluded that those who used marijuana the longest (six or more years) were twice as likely to develop schizophrenia or delusional disorders. They also were four times more likely than non-users to score highly on a test gauging psychotic-like experiences.
Higher scores on the test also were seen among those who used marijuana for less than three years.
The study was published online in the Archives of General Psychiatry.