Psychiatric disorders
From a diagnostic standpoint, organic disorders were believed to be caused by physical illness affecting the brain (that is, psychiatric disorders secondary to other conditions) while functional disorders were considered disorders of the functioning of the mind in the absence of physical disorders (that is, primary psychological or psychiatric disorders). Subtle physical abnormalities have been found in illnesses traditionally considered functional, such as schizophrenia. The DSM-IV-TR avoids the functional/organic distinction, and instead lists traditional psychotic illnesses, psychosis due to general medical conditions, and substance-induced psychosis.

Primary psychiatric causes of psychosis include the following:

schizophrenia
mood disorders, including psychotic depression,bipolar disorder in the manic and mixed episodes of bipolar I disorder and depressive episodes of both bipolar I and bipolar II
schizoaffective disorder
delusional disorder
brief psychotic disorder
schizophreniform disorder

Schizotypal personality disorder
Certain personality disorders in times of stress (including paranoid personality disorder, schizoid personality disorder, and borderline personality disorder)
Post-traumatic stress disorder
Shared delusional disorder
Sometimes in obsessive–compulsive disorder (OCD)
Dissociative disorders, due to many overlapping symptoms. It is also important to note that those with dissociative disorders may be more vulnerable to psychotic symptoms due to the disconnect from reality that is already experienced. Careful differential diagnosis includes especially dissociative identity disorder.