I have no idea about psychosis and pot. I do know every single serious pot user I have ever been around ends up with a dead brain. I mean dead, there is no there, there. I know tons of people that dabbled and are fine but the serious users have no brain left.
I believe this. My parents often say the same. My generation however...it's much harder to tell. Too many dead brains, and they can't all be caused by serious mj use.