What is depression? Depression is a mood disorder, a syndrome characterized by markedly low mood and/or diminished interest and absence of pleasantness; symptoms lasting more than 2 weeks; impaired social functioning with distress or adverse consequences for the person; not caused by brain disease or alcohol or drug use. Depression has 9 characteristics: 1. Depressed will for most of the day, almost every day, evidenced by two ways, one is subjective expression (e.g., feeling empty, helpless, sad, etc.) and the other is observation by others (love of crying, etc.); adolescents show inexplicable impatience of mood; 2. For most of the day, a distinct feeling of all things or almost all matters little interest or disinterest, almost daily (as evidenced by their own subjective expressions, and the feelings of others); 3. significant weight loss without dieting, or weight gain (e.g., more than 5% change in weight in a month), or increased appetite, or decreased appetite, almost daily; 4. difficulty falling asleep, not sleeping deeply, dreaming a lot, waking early, or sleepiness, almost daily; 5. agitation 5. agitation, or unresponsiveness, almost daily (as evidenced by one’s own subjective expressions, and the feelings of others); 6. fatigue or lethargy, almost daily; 7. feeling worthless or feeling excessive and inappropriate guilt about oneself or one’s environment, almost daily, not only because of self-blame or guilt over illness; 8. decreased ability to think or concentrate, or hesitation 8. Decreased ability to think or concentrate, or hesitation, almost daily (evidenced by one’s own subjective expressions, and by the feelings of others); 9. Recurrent thoughts of death (not only fear of death), recurrent suicidal thoughts without a clear plan, or attempted suicide, or a clear plan to commit suicide.