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Any of several serious mental illnesses characterized by defects in judgment and other cognitive processes and by loss of contact with reality. Psychoses can be divided into two major types: functional and organic. Functional psychoses include schizophrenia and affective disorders (also called mood disorders), such as major depressive disorder and bipolar disorder. Organic psychoses arise secondary to a preexisting medical condition such as Alzheimer disease and share important features with functional psychoses. Certain medications, including narcotics (used to treat pain) and levodopa (used to treat Parkinson disease), can cause symptoms of psychoses. The major symptoms, aside from delusions and hallucinations, are disorganized speech and behaviour, lack of emotional expression, and apathy. Treatment usually consists of medication and psychotherapy; severe cases may require permanent hospitalization. Compareneurosis.
This entry comes from Encyclopædia Britannica Concise. For the full entry on psychosis, visit Britannica.com.