I think this is a classic case of correlation does not imply causation. As someone that has known these people, and I does smoke as an adult, I would interpret that as people who are struggling with mental illness symptoms turn to weed as an outlet. Especially when we take it with the wider literature on drug abuse and mental illness any practitioner worth their salt knows mental illness makes drug abuse more likely and yes then the two affect one another which is why rehab is usually a big part of the hospitalization process. But what I don't want to see is more moral panic so we can renew the war on drugs which as always should really be the war on poverty and mental health issues.