Schizophrenia is the most common psychotic disorder. People with this disorder usually have hallucinations and/or delusional thinking plus disorganized speech that persists more than 6 months. Doctors and researchers often talk about three types of symptoms: positive, negative, and cognitive. Positive symptoms are the psychotic symptoms that can be observed, such as delusions and hallucinations. Negative symptoms are also called deficit symptoms. These are things that the patient is lacking or limited in, such as diminished speech, decreased range of affect, and limited interests/pleasure. Cognitive symptoms are impairments in executive functions such as insight and judgment. It is the negative and cognitive symptoms that cause functional impairment.
Schizophreniform disorder is diagnosed when an individual has symptoms of schizophrenia that last less than 6 months.
Schizoaffective disorder is diagnosed when people have pronounced symptoms of a mood disorder (depression or mania) along with positive symptoms of schizophrenia, such as hallucinations or delusional thinking. The psychotic symptoms of schizoaffective disorder tend to come and go, but they persist in schizophrenia. The diagnosis of schizoaffective disorder requires the presence of psychotic symptoms for at least a few weeks, even when the individual is not experiencing mania or depression. People with the depressive form of this illness experience mainly depression. People with bipolar schizoaffective disorder experience both mania and depression.
Psychosis can occur in those with bipolar disorder during depressive and manic episodes, but it most common during manic episodes. During a manic episode, people with this disorder may have grandiose delusions. During depressive episodes, the individual may have paranoid delusions. In both cases, delusions may be accompanied by auditory or visual hallucinations (and, less commonly, hallucinations of taste or feeling). The difference between bipolar disorder with psychotic features and schizoaffective disorder is that people with schizoaffective disorder may experience delusions or hallucinations without a change in mood. In bipolar individuals, psychosis is always accompanied by a mood change.
An individual can react with a short psychotic episode to an extremely stressful event. It usually lasts less than a month and does not return.
Use of, or withdrawal from, substances like alcohol and methamphetamines can result in psychotic delusions and hallucinations.
Brain tumors or other illnesses can sometimes result in psychosis.