Almost half of American adolescents experience at least one mental disorder, over a fourth experience a severely impairing one, and at least a fifth experience a severely impairing one other than a substance use disorder, a new study has found.

This appears to be the first nationally representative study of the subject.

The research team was headed by Kathleen Merikangas, Ph.D., a senior investigator and chief of the Genetic Epidemiology Research Branch of the National Institute of Mental Health. Results appeared in the October Journal of the American Academy of Child and Adolescent Psychiatry.

The design consisted of face-to-face interviews of a nationally representative sample of more than 10,000 adolescents aged 13 to 18, with an average age of 15. The interview instrument used was a modified version of the World Health Organization Composite International Diagnostic Interview Version 3.0. During the interviews, the youth were asked whether they had ever experienced symptoms of various DSM-IV anxiety, mood, behavior, substance use, or eating disorders. Parents of the subjects also filled out questionnaires to provide additional information about their offspring's mental and physical health as well as sociodemographic characteristics.

In addition to the results noted above, the data showed that anxiety disorders were the mental illnesses most commonly experienced by subjects at some point in their lives. Anxiety disorders had affected 32 percent of subjects, behavior disorders had affected 19 percent, mood disorders had affected 14 percent, substance use disorders had affected 11 percent, and eating disorders had affected 3 percent.

The average age of onset for disorder classes was earliest for anxiety at 6 years, followed by age 11 for behavior disorders, age 13 for mood disorders, and age 15 for substance use disorders.

Subjects whose parents were not college graduates were at increased risk for all disorder classes. In addition, the lifetime prevalence rates for anxiety disorders, behavior disorders, and substance use disorders were higher for respondents whose parents were divorced or separated than for those whose parents were married or cohabiting.

However, family income level and urbanicity were not associated with any of the classes of mental disorders.

"The results of this study are consistent with previous results," David Fassler, M.D., a child and adolescent psychiatrist and clinical professor of psychiatry at the University of Vermont, told Psychiatric News. "The findings confirm that more than one adolescent in five will experience significant signs and symptoms of mental illness. The study also underscores our growing awareness that many, if not most, psychiatric disorders begin well before adulthood. The good news is that we can help almost all of these young people. The real tragedy is that the majority don't receive the effective and appropriate treatment they need and deserve."

An abstract of "Lifetime Prevalence of Mental Disorders in U.S. Adolescents: Results From the National Comorbidity Study—Adolescent Supplement" is posted at <www.jaacap.com> under the October issue.