About 2.2 million adolescents ages 12 to 17 (9 percent) suffered at least one major depressive episode in the past year. These adolescents were more than twice as likely to have used illicit drugs in the past month than their peers who had not experienced a major depressive episode.

For the survey that asked respondents questions about lifetime and past major depressive episodes or experiences, researchers used Diagnostic and Statistical Manual of Mental Disorders (DSM-IV).

The criteria in the DSM-IV specifies a period of two weeks or longer during which there is either depressed mood or loss of interest or pleasure and at least four other symptoms that reflect a change in functioning, such as problems with sleep, eating, energy, concentration and self-image.

Substance Abuse and Mental Health Services Administration Charles Curie says, "If parents have concerns about their child's behavior or emotions, they should discuss their concerns with their doctors, teachers, counselors, social workers, spiritual advisors, friends, or relatives who know about child development and mental health. Ask for help in finding out what the problem is and where to get services. Unfortunately, less than half of these children received any help for their depression."