Schizophrenia is a mental disorder characterized by abnormal social behavior and failure to understand what is real. Common symptoms include false beliefs, unclear or confused thinking, hearing voices that others do not hear, reduced social engagement and emotional expression, and a lack of motivation. People with schizophrenia often have additional mental-health problems such as anxiety disorders, major depressive illness, or substance-use disorders. Symptoms typically come on gradually, begin in young adulthood, and last a long time. The causes of schizophrenia include environmental and genetic factors. Possible environmental factors include being raised in a city, cannabis use, certain infections, parental age, and poor nutrition during pregnancy.