A few random gibberings from a family physician who has worked with many schizophrenics, studied schizophrenia with much fascination, used serotonergic psychedelics, and has (cautiously) used dissociatives to try to get into the mindset of the schizophrenic and the manic:
First of all, it amazes me how much vitriol this topic stirs up in the psychonaut community. I think this is because it comes dangerously close to two highly divisive debates:
1) In modern, progressive-thinking, culturally Western psychedelic-drug-using communities, who place a high premium on harm reduction and minimal tension with the larger society, what -- if any -- place is there for spirituality?
2) In the name of minimizing harm to individuals and negative reputation for the group, does it behoove psychedelic-drug-using communities to exclude, or at the very least discourage, people whom the mainstream medical community has deemed not mentally competent to make medical decisions for themselves?
From my own readings and drug-taking, I have tentatively concluded that hole-dose ketamine produces about the closest headspace to catatonic schizophrenia that a mentally healthy individual can achieve. Threshold dose ketamine or second-plateau DXM in the setting of amphetamine-induced sleep deprivation, meanwhile, put me in a headspace that reminds me very much of paranoid schizophrenia. In other words, I think dissociatives (especially those with a DA agonist component, or taken along with DA agonists) provide a far better model of schizophrenia than any 5ht agonists (yes yes, smartasses, I'm aware that DXM is a middling SNRI also!)
That said, dissociative use and schizophrenia are qualitatively different in one aspect that cannot be replicated in a non-schizophrenic individual: Schizophrenia is life-long. A schizophrenic never "comes down" out of this state of feeling like an emotionally flat automaton in a threatening outer world that feels fake (and to their reckoning, probably is fake). They have fully integrated this perceptive state into their worldview, and know no differently. It is this integration which, doctors think, gives rise to their social isolation, delusions, hallucinations, and constant state of fear and high-alert. Dissociative users, by contrast, are well aware, at least when they're not at the peak of a trip, that this feeling of weirdness and fakeness that the world takes on is entirely a drug effect. As such it usually doesn't strongly influence their sober worldview, the major choices they make in life, or how they [fail to] relate to other people. In fact, in my experience dissociative users (and to a lesser degree serotonergic psychedelic users) who take their trip-induced visions too seriously, or use them as a guide to how to live their sober lives, tend to be treated as something of an embarrassment by the psychonaut community.