Using cannabis raises the risk of teenagers developing a psychotic disorder by a staggering 11 times compared to teens who didn't report using the drug, a Canadian study has found. That's a much stronger association than what previous studies have reported. A 2016 analysis of data from 10 different studies found the heaviest cannabis users were about four times more likely than non-users to be diagnosed with schizophrenia or another psychotic condition. Part of the reason, aside from cannabis users' age, is that much of the data used in past analyses of adolescent cannabis use comes from before 2000, when cannabis was far less potent than it is today, the team behind the new analysis suggests.