Depression may be the result rather than the cause of risky teen behaviors.

A new study shows that teen sex or drug use raised the risk of depression a year later.

Researchers say the results challenge the notion that teens become sexually active or engage in drug use to “self-medicate” their own depression.

"Findings from the study show depression came after substance and sexual activity, not the other way around," says researcher Denise Dion Hallfors of the Pacific Institute for Research and Evaluation, in a news release.

Teen Minds: What Are They Thinking?

Sex, Drugs Come First and Depression Follows

In the study, published in the American Journal of Preventive Medicine, researchers analyzed data from a national survey of more than 13,000 teenagers in grades seven to 11 who were interviewed in 1995 and again a year later.

Overall, the results showed that sex and drug use was associated with an increased risk of depression by the second interview, but depression didn’t predict risky behavior.

Researchers say both drug experimentation and sexual activity were linked to an increased risk of future depression in teenaged girls. Among teenage boys, only high-risk behaviors, such as binge drinking, were associated with an increase in future depression.

For example:

Girls who had experimented with drugs and sex were two to three times more likely to become depressed than those who abstained. Boys who used marijuana were more than three times as likely to become depressed as nonusers. Boys who engaged in binge drinking were nearly five times more likely to become depressed than abstainers.

Depression Hits 1 in 10 Teen Girls Each Year

Depression Still Raises Risks

Though depression did not influence risky behavior among teenaged boys, researchers found depression was related to behavior in some cases among teenage girls.

Specifically, depression reduced the likelihood of high-risk behavior among girls who abstained from drug and alcohol use but increased the risk of these behaviors among girls already experimenting with drugs and alcohol.

"For females, even modest involvement in substance use and sexual experimentation elevates depression risk," write the researchers. "In contrast, boys show little added risk with experimental behavior, but binge drinking and frequent use of marijuana contribute substantial risk."

Researchers say the results show that experimentation with substance use and sex, along with other factors, such as dropping grades in school and social isolation, can be signs of depression in teenagers that parents and health care professionals should look out for.

Identifying Teen Depression

Young people with depression may have a hard time coping with everyday activities and responsibilities, have difficulty getting along with others, and suffer from low self-esteem.

Depression is more than just having the "blues" now and then; it is a persistent condition.

Here are some signs and symptoms of depression to look out for:

—Frequent sadness, tearfulness, or crying

—Hopelessness

—Decreased interest in activities or inability to enjoy former favorite activities

—Persistent boredom; low energy

—Social isolation; poor communication

—Low self-esteem and guilt

—Extreme sensitivity to rejection or failure Increased irritability, anger, or hostility

—Difficulty with relationships Frequent complaints of physical illness such as headaches and stomachaches Frequent absences from school or poor performance in school

—Poor concentration

—A major change in eating and/or sleeping patterns

—Talk of or efforts to run away from home

—Thoughts or expressions of suicide or self-destructive behavior

Teen Emotional Problems Go Unnoticed

By Jennifer Warner, reviewed by Michael W. Smith, MD

SOURCES: Hallfors, D. American Journal of Preventive Medicine, October 2005; vol 29. News release, Health Behavior News Service. Substance Abuse and Mental Health Administration.