What are the symptoms of major depressive disorder?

Major depressive disorder requires at least five symptoms present during the same two-week period, with at least one being depressed mood or loss of interest or pleasure in previously enjoyed activities. Other symptoms include significant weight change or appetite change, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue or loss of energy, feelings of worthlessness or excessive guilt, difficulty concentrating or making decisions, and recurrent thoughts of death or suicidal ideation.