Major depressive disorder refers to a well-defined group of symptoms. For an episode to be considered a major depressive disorder it must present with five or more of the following symptoms, present during most of the day, nearly every day, for a minimum of two consecutive weeks. At least one symptom must be either depressed mood or loss of interest or pleasure. The other symptoms include insomnia or hypersomnia, change in appetite or weight, psychomotor retardation or agitation, low energy, poor concentration, thoughts of worthlessness or guilt, and recurrent thoughts about death or suicide.
More Answers from Univ. of Nev. School of Medicine, Family Medicine