I would imagine that psychosis and certain psychedelic states have some similarities. But schizophrenia is very debilitating and often there is certain things going on in the brain that are qualitatively different then a typical psychedelic agent. Pyschedelics certainly can make one lose touch with reality but the good thing is its usually temporary unless you were slipping anyway. I don't think the idea that these substances endogenous production can go haywire and make certain aspects of psychosis what they are is totally unfounded.