Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behavior, feelings, and sense of well-being. A depressed mood is a normal temporary reaction to life events such as loss of a loved one. It is also a symptom of some physical diseases and a side effect of some drugs and medical treatments. Depressed mood is also a symptom of some mood disorders such as major depressive disorder or dysthymia. People with a depressed mood may be notably sad, anxious, or empty; they may also feel notably hopeless, helpless, dejected, or worthless. Other symptoms expressed may include senses of guilt, irritability, or anger. Further feelings expressed by these individuals may include feeling ashamed or an expressed restlessness. These individuals may notably lose interest in activities that they once considered pleasurable to family and friends or otherwise experience either a loss of appetite or overeating. Experiencing problems concentrating, remembering general facts or details, otherwise making decisions or experiencing relationship difficulties may also be notable factors in these individuals' depression and may also lead to their attempting or actually dying by suicide.

Management of depression may involve a number of different therapies: medications, behavior therapy, and medical devices. Major depressive disorder, often referred to simply as "depression", is diagnosed more frequently in developed countries, where up to 20% of the population is affected at some stage of their lives. According to WHO (World Health Organization), depression is currently fourth among the top 10 leading causes of the global burden of disease; it is predicted that by the year 2020, depression will be ranked second. Though psychiatric medication is the most frequently prescribed therapy for major depression,[3] psychotherapy may be effective, either alone or in combination with medication.[4] Combining psychotherapy and antidepressants may provide a "slight advantage", but antidepressants alone or psychotherapy alone are not significantly different from other treatments, or "active intervention controls". Given an accurate diagnosis of major depressive disorder, in general the type of treatment (psychotherapy and/or antidepressants, alternate or other treatments, or active intervention) is "less important than getting depressed patients involved in an active therapeutic program." Psychotherapy is the treatment of choice in those under the age of 18, with medication offered only in conjunction with the former and generally not as a first line agent. The possibility of depression, substance misuse or other mental health problems in the parents should be considered and, if present and if it may help the child, the parent should be treated in parallel with the child.