I’m in two minds about this, on the one hand I spent a week with acute psychosis after smoking weed when I was a teenager, so I really think people have to be more aware of the risks. On the other hand, I think it’s clear that this is not a perfect research design, and there are obvious possible confounds.

What about legalisation as a natural experiment? Has anyone done diff-in-diffs of US states and simply looked at eg mental health diagnoses or hospital admissions?