Which comes first in adolescence--sex and drugs or depression?

BACKGROUND: The notion that adolescents "self-medicate" depression with substance use and sexual behaviors is widespread, but the temporal ordering of depression and these risk behaviors is not clear. This study tests whether gender-specific patterns of substance use and sexual behavior precede and predict depression or vice versa.
METHODS: Data are from the National Longitudinal Study of Adolescent Health, weighted to produce population estimates. The sample includes 13,491 youth, grades 7 to 11, interviewed in 1995 and again 1 year later. Multivariate logistic regression analyses, conducted in 2004, tested temporal ordering, controlling for covariates. The main outcome measures were depression, as measured by a modified Center for Epidemiological Studies-Depression Scale (CES-D), and three behavior patterns: (1) abstaining from sexual intercourse and drug use, (2) experimental behavior patterns, and (3) high-risk behavior patterns.
RESULTS: Overall, sex and drug behavior predicted an increased likelihood of depression, but depression did not predict behavior. Among girls, both experimental and high-risk behavior patterns predicted depression. Among boys, only high-risk behavior patterns increased the odds of later depression. Depression did not predict behavior in boys, or experimental behavior in girls; but it decreased the odds of high-risk behavior among abstaining girls (RRR = 0.14) and increased the odds of high-risk behavior (RRR = 2.68) among girls already experimenting with substance use.
CONCLUSIONS: Engaging in sex and drug behaviors places adolescents, and especially girls, at risk for future depression. Future research is needed to better understand the mechanisms of the relationship between adolescent behavior and depression, and to determine whether interventions to prevent or stop risky behaviors will also reduce the risk of later depression.