I'm sorry. Pot has never been shown to cause schizophrenia! There is some question as to schizophrenia and early pot use having correlation, but not causality. Virtually all institutionalized schizophrenics smoke cigarettes, most likely because nicotine relieves some of the underactive cholinergic response seen in schizophrenics. Just because A and B occur together says nothing about whether A causes B or B causes A or neither; double blind studies are required for statistical causality to be determined within the agreed upon confidence interval..
And marijuana most definitely has medicinal effects including possible anti-cancer effects by activating NKC (Natural Killer Cells).