Depression: Clinical and Research PerspectivesAbout This Hardback Depression is a condition that results in low mood and aversion to activity. It can be long term and short term. Depression can cause sadness, difficulty in thinking and concentration, a feeling of dejection and hopelessness. It also affects a person's behavior, thoughts, motivation, feelings, and sense of well being. Some factors that cause depression are life events, gender identity and sexuality, medical treatment and substance