Freud thought this was a physical brain disorder. In the personality disorders, Cluster A, is the category for 'Odd". Oddness refers to difference from the normal. All over the world the 'incidence' of schizophrenia is about 1 %. That almost suggests that the human tolerance for deviation is that. Over that imaginary line, the oddness is considered schizophrenic deviation. In recent years in roads have been made into that wilderness though. 20 years ago with the advent of newer mood disorder medications and a change in philosophy of mental illness, increasing numbers of patients were tried on mood disorder medications with many diagnosis changed from schizophrenia to schizoaffective or bipolar. They were said to have a better prognosis.
The odd group becomes odder by isolation. When the oddness goes over the top it's called 'psychosis'. When the 'psychosis' persists or recurs it's called schizophrenia. The French were more tolerant than the Americans who were quick to diagnosis schizophrenia especially in the young. The French said that the psychosis must persist 6 month to a year before the diagnosis was made. The Americans were almost recruiting for schizophrenia with the inherent conflict of interest that the diagnosis of schizophrenia meant a life time of medications and severe social marginalization. The French in contrast with their stronger family ties and greater tolerance for deviance said 'wait and see'.
Today that's the position that's held. Increasingly young adults are seen to be prone to "brief psychotic episodes" under high stress and if these are treated appropriately need not progress to schizophrenia.
Historically, the use of drugs and alcohol were considered a 'sympton' of mental disorder. Now that chicken and egg argument has been resolved in favour of drugs and alcohol as the primary disease with mental illness following from continued 'chemical brain damage' at first reversible and later irreversible. So much of the 'schizophrenia' of yesteryear is today recognized as chronic marijuania, chronic cocaine, chronic alcoholism. The drugs and alcohol disrupt the mechanisms for modulation of mood and cognitive functions. Chronic abuse of drugs and alcohol is increasingly odd especially coupled with isolation.
Unfortunately the medication used for schizophrenia while initially beneficial can if not used judiciously cause it's own set of problems. The tardive dyskenesia was the worst of these, but the 'thorazine shuffle' of extrapyramidal side effects was definitely alienating. Many patients describe the loss of self and incapacity to think and while the pharmacist might say that was due to the medication the clinician recognizes that successful treatment of schizophrenia doesn't require a medication that causes that dehumanization. The newer medications are much more appreciated. They're all major tranquillizers, treating the deap seated anxiety, associated with the depersonalization, and alienation that goes with experiencing hallucinations or having delusions.
The medications are quite amazing as they take a person hearing voices threatening and accusing them and cause those voices to go, leaving the person at last able to think. Some delusions are more sensitive to medications and once the extreme crisis are over the person can be rehabilitated through therapeutic communities where social skills and relearning of the often lost capacity to relate is addressed. A lot of schizophrenia is social phobia. The tendency of the patient to hide in the 'safety' of the attic is unfortunately often what keeps them ill because it's only in association with others they can repair the central damage to the ability to interpersonally interact.
Yet the patient will so often be phobic of the complexity of cues coming from people and social settings with much the same hypersensitivity that the agoraphobic describes. Unfortunately, "if you don't use it, you lose it" and learning from rehabilitation medicine modern schizophrenia treatment has been increasingly successful through therapeutic communities coupled with medications which increasingly are more tolerable and provide excellent symptom resolution without side effects.