I believe that psychiatry as a field has not emphasized this point sufficiently. As a result, some patients have been harmed by the very treatments that were supposed to help them; or to the disgrace of psychiatry, harmed and then misdiagnosed. Substance-induced psychosis should also be ruled out. Both substance- and medication-induced psychosis can be excluded to a high level of certainty while the person is psychotic, typically in an emergency department, using both a

Broad spectrum urine toxicology screening, and a
Full serum toxicology screening (of the blood).Some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests. So a psychotic persons family, partner, or friends should be asked whether he or she is currently taking any dietary supplements.Common mistakes made when diagnosing psychotic patients include:
Not properly excluding delirium,
Missing a toxic psychosis by not screening for substances and medications,
Not appreciating medical abnormalities (e.g., vital signs),
Not obtaining a medical history and family history,
Indiscriminate screening without an organizing framework,
Not asking family or others about dietary supplements,
Premature diagnostic closure, and
Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder.Schizoaffective disorder can only be diagnosed among those who have undergone a clinical evaluation with a psychiatrist. The criterion includes mental and physical symptoms such as, hallucinations or delusions, and depressive episodes. There are also links to bad hygiene and a troubled social life for those with schizoaffective disorder. Research has failed to conclusively demonstrate a positive relationship between schizoaffective disorder and substance abuse.
A poor prognosis was assumed to apply to these patients by most clinicians, and this poor prognosis was harmful to many patients. The poor prognosis for DSM-IV schizoaffective disorder was not based on patient outcomes research, but was caused by poorly defined criteria interacting with clinical tradition and belief; clinician enculturation with unscientific assumptions from the diagnosis history (discussed above), including the invalid Kraepelinian dichotomy; and by clinicians being unfamiliar with the scientific limitations of the diagnostic and classification system.The DSM-5 schizoaffective disorder workgroup analyzed all of the available research evidence on schizoaffective disorder, and concluded that "presenting symptoms of psychosis have little validity in determining diagnosis, prognosis, or treatment response." Given our understanding of overlapping genetics in bipolar disorders, schizoaffective disorder, and schizophrenia, as well as the overlap in treatments for these disorders; but given the lack of specificity of presenting symptoms for determining diagnosis, prognosis or treatment response in these psychotic illness syndromes, the limits of our knowledge are clearer: Presenting symptoms of psychosis describe only presenting symptoms to be treated, and not much more. Schizoaffective disorder was changed to a longitudinal or life course diagnosis in DSM-5 for this reason. Research
Little is known of the causes and mechanisms that lead to the development of schizoaffective disorder.