Which mental illness is characterized by low mood, low self-esteem, loss of interest or pleasure?

Major depressive disorder (MDD), also known simply as depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, loss of interest or pleasure in normally enjoyable activities. Those affected may also occasionally have delusions or hallucinations.

The diagnosis of major depressive disorder is based on the person's reported experiences and a mental status examination. There is no laboratory test for the disorder. Those with major depressive disorder are typically treated with psychotherapy and antidepressant medication.

Major depressive disorder is believed to be caused by a combination of genetic, environmental, and psychological factors, with about 40% of the risk being genetic. Risk factors include a family history of the condition, major life changes, certain medications, chronic health problems, and substance use disorders. It can negatively affect a person's personal life, work life, or education as well as sleeping, eating habits, and general health. Major depressive disorder affected approximately 163 million people (2% of the world's population) in 2017.