Psychosis is a symptom or feature of mental illness typically characterized by radical changes in personality, impaired functioning, and a distorted or nonexistent sense of objective reality.
Patients suffering from psychosis have impaired reality testing; that is, they are unable to distinguish personal subjective experience from the reality of the external world.
They experience delusions that they believe are real, and may behave and communicate in an inappropriate and incoherent fashion. Psychosis may appear as a symptom of a number of mental disorders, including mood and personality disorders. It is also the defining feature of schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, and the psychotic disorders (i.e., brief psychotic disorder, shared psychotic disorder, psychotic disorder due to a general medical condition, and substance-induced psychotic disorder).
With regard to substance abuse, several different research groups reported in 2004 that cannabis (marijuana) use is a risk factor for the onset of psychosis.
Psychotic symptoms and behaviors are considered psychiatric emergencies, and persons showing signs of psychosis are frequently taken by family, friends, or the police to a hospital emergency room. A person diagnosed as psychotic can be legally hospitalized against his or her will, particularly if he or she is violent, threatening to commit suicide, or threatening to harm another person. A psychotic person may also be hospitalized if he or she has become malnourished or ill as a result of failure to feed, dress appropriately for the climate, or otherwise take care of him- or herself.