I think the issue is that someone who is predisposed to schizophrenia might not be aware that this is the case. Also, we already know that drug use can have pe

I think the issue is that someone who is predisposed to schizophrenia might not be aware that this is the case. Also, we already know that drug use can have permanent effects that presumably would not have manifested if the person had not taken drugs, unless you think that people who didn't see hallucinations before LSD and see hallucinations after LSD would have started seeing hallucinations anyway. So I don't see why it would be unreasonable to think that drug use can trigger an onset of schizophrenia in an already predisposed person that would have not happened otherwise.