Schizophrenia is a chronic mental illness that causes changes in thinking, perception, emotions, language, sense of self and behavior. Common symptoms include hallucinations, delusions, disorganized speech and behavior, lack of motivation and impaired cognitive skills. It is diagnosed through medical exams, history, lab tests and ruling out other potential causes. While the causes are not fully understood, genetics and environmental factors like stress, drug use and complications during birth are thought to play a role.