Just one person's anecdote, but I am close with a person who is schizophrenic. Marijuana use significantly contributed to episode occurrence. After their psychologist told them that it can make things worse, they stopped, and it improved their situation considerably.

I think it's related to the whole paranoia side of things.

This is a valid point, and more work needs to be done in this field.

However I think a fairly safe default is to tell kids not to smoke pot until we can make a more educated decision (provided of course we don't extend that ban to adults for no reason, and provided we don't purposely ruin the lives of kids who don't listen. (You wouldn't arrest or kick a kid out of school for smoking tobacco.)).

Or even more simply: is there something in marijuana that makes schizophrenia more tolerable than with alcohol. Furthermore, mentally ill people are going to have more trouble finding a regular pot dealer, the black market being an inherently suspicious place, so as their condition worsens alcohol becomes the most-available drug.