Psychosis refers to symptoms such as delusions, hallucinations, disorganized thinking and speech, and bizarre and inappropriate motor behavior (including catatonia) that indicate loss of contact with reality. (See also Introduction to Schizophrenia and Related Disorders.)
Shared psychosis (previously termed folie à deux) is now considered a subset of delusional disorder. It is a rare disorder that usually occurs in a person or group of people (usually a family) who are related to a person with a significant delusional disorder. The socially dominant member in the relationship has the primary disorder and imposes the delusion on or convinces the less dominant person (or people) in the relationship of the unusual beliefs.
Doctors try to identify the person in the relationship who has the primary psychosis, because the person with the secondary disorder typically does not maintain the delusional beliefs when separated from the person with the primary disorder. Counseling and therapy can usually help people who have a shared psychosis. Psychotic symptoms are treated with antipsychotic drugs as needed.