Schizophrenia is a mental illness characterized by relapsing episodes of psychosis. Major symptoms include hallucinations, delusions, and disorganized thinking. Other symptoms include social withdrawal, decreased emotional expression, and lack of motivation. Symptoms typically come on gradually, begin in young adulthood, and in many cases never resolve. There is no objective diagnostic test; diagnosis is based on observed behavior, a history that includes the person's reported experiences, and reports of others familiar with the person. To be diagnosed with schizophrenia, symptoms and functional impairment need to be present for six months. Many people with schizophrenia have other mental disorders that may include an anxiety disorder such as panic disorder, obsessive-compulsive disorder, depressive disorder, or a substance use disorder.