Schizophrenia is a mental illness characterized by psychosis of recurrent episodes.  The main symptoms include hallucinations (often hearing voices), delusions (having beliefs not shared by others), and disorganized thinking.  Other symptoms include social withdrawal, decreased emotional expression and lack of motivation. Symptoms often appear gradually, early adulthood and, in many cases, never go away. There is no objective diagnostic test; The diagnosis is based on the observed behavior, a story that involves the person's reported experiences and relationships with other people. To be diagnosed with schizophrenia, symptoms and functional disorders must be present for six months (DSM-5) or one month (ICD-11).  Many people with schizophrenia have other mental disorders such as panic disorder, obsessive-compulsive disorder, depressive disorder, or substance use disorder.

About 0.3% to 0.7% of people are affected by schizophrenia during their lifetime.  In 2017, there were approximately 1.1 million new cases and 2019, a total of 20 million cases worldwide.  Men are more often affected and their appearance is above average. The causes of schizophrenia include environmental and genetic factors. Possible environmental factors include increased adolescence, infections, age of a person's parents, and poor nutrition during pregnancy. Genetic factors include a variety of common and rare genetic variants.