Psychosis: In the general sense, a mental illness that markedly interferes with a person's capacity to meet life's everyday demands. In a specific sense, it refers to a thought disorder in which reality testing is grossly impaired. Symptoms can include seeing, hearing, smelling, or tasting things that are not there; paranoia; and delusional thoughts. Depending on the condition underlying the psychotic symptoms, symptoms may be constant or they may come and go. Psychosis can occur as a result of brain injury or disease, and is seen particularly in schizophrenia and bipolar disorders. Psychotic symptoms can occur as a result of drug use, but this is not true psychosis. Diagnosis is by observation and interview. Treatment is with neuroleptic medication, either the newer, safer, atypical neuroleptics like risperidone (brand name: Risperdal) or the older neuroleptics like haloperidol (brand name: Haldol.) In cases that do not respond to medication, electroshock therapy (ECT) is sometimes valuable.