"There is a well-documented link between cannabis and the onset of psychosis in vulnerable individuals. Typically, guidelines recommend that people w/a history of mental illness, either individually or in their family, should avoid cannabis at all costs." https://www.leafly.com/news/health/marijuana-mental-health-harm-reduction-strategies

2/(From a cannabis company--even they admit the problem.
"Approximately 1 in 5 Canadians and Americans experience a mental health condition each year, and approximately 1 in 33 Canadians will experience psychosis in their lifetime, with similar numbers in the States." @SenWarren