>>5240625>If you are already prone to psychosis weed can trigger an episode""But what is also clear, if you do have a vulnerability to schizophrenia and you smoke [cannabis]," Volkow says, "it's likely to trigger an episode. It's likely to advance the [disease]." She says when people with certain risky genes associated with psychosis smoke, the risk of developing schizophrenia goes up sixfold, according to a 2005 study. But for someone without those genes, Volkow says the evidence suggests "you can smoke all the marijuana you want and it will make no difference whatsoever.""
"One thing to note, Lisdahl says, is that more people smoke cannabis today than ever in history. If the connection between weed and schizophrenia is solid, then the number of people with schizophrenia should also be going up. But it hasn't. The fraction of people who have the disorder still hovers at around 1 percent."
https://www.npr.org/sections/health-shots/2015/03/06/390143641/pot-can-trigger-psychotic-symptoms-for-some-but-do-the-effects-last 
