Psychological disorder: what makes a behavior “abnormal”? Abnormal psychology studies mental disorders to understand and treat them. People with psychological disorders experience significant distress due to dysfunctional patterns of thought, emotion, and behavior that are considered deviant in their culture. Psychological disorders are out of a patient's control and may be treated with drugs or therapy, like other medical disorders. They have both biological and environmental influences, reflecting the bio-psycho-social model of illness.