Can excessive marijuana use lead to psychosis?

Correlation is not the same as causation
The Globe and Mail (Canada)
Wednesday, April 11, 2018

Psychosis is quite rare – fewer than three in 100 people will experience a psychotic episode in their lifetime. People who smoke or otherwise consume cannabis, especially in significant quantities, have a higher incidence. Some people have vulnerability, a genetic predisposition to psychosis, and cannabis can be a trigger, as can other things like trauma or amphetamines. Severe mental illness like schizophrenia tends to arise in late teens and early adulthood, the same time young people tend to experiment with drugs, so the psychosis can be coincidental. Finally, many people with severe mental illnesses that feature psychotic episodes self-medicate, with cigarettes, alcohol and cannabis.