Sex and Drugs

What are the two most terrifying words for parents of teenagers? Sex and drugs. In fact, most youth in the US begin having sex and using drugs during the teen years. An enduring question, though, is whether these two behaviors are linked. Specifically, does having sex for the first time make teens more likely to use drugs?

We know from prior research that early sexual activity is associated with the use of intoxicating substances, such as alcohol and marijuana. However, it is not immediately clear why.

One possibility is that having sex for the first time (i.e., sexual debut) sets in motion a series of developmental processes that lead to increased drug and alcohol use. For example, once youth are sexually active, they may spend more time with older, sexually active peers in a social milieu that involves greater access to substances, and more pressure to use them.

Another possibility is that the association between sexual debut and substance use is simply a coincidence of timing. In the US, sexual activity and substance use often begin around the same time, and typically increase across adolescence. Consequently, associations between the two behaviors may be spurious, reflecting general developmental trends in the population.

Finally, it is possible that some youth are more predisposed to engage in risky behaviors of all kinds (e.g., due to poor self-control or some other factor), and these youth are the ones having sex and doing drugs at an earlier age. Thus, the association between sexual debut and substance use could reflect differences between youths’ general behavioral tendencies, not the direct influence of sexual debut on substance use.

From a public health perspective, it important to know which of these three explanations is correct. If sexual debut directly increases risk for substance use, then interventions aimed at preventing early sexual debut could reduce drug and alcohol use, but if the association is coincidental, these same interventions will have no effect. If both behaviors are due to some underlying behavioral propensity, then interventions should target this propensity to prevent both early/risky sexual behavior and drug use.

Thus, the association between sexual debut and substance use could reflect differences between youths’ general behavioral tendencies, not the direct influence of sexual debut on substance use.

In our study, we attempted to disentangle these three explanations using data from the California Families Project, an ongoing longitudinal study of 674 Mexican-origin youth who were interviewed annually from age 10 to age 18. The availability of longitudinal data across a nine-year time span allowed us to simultaneously test all three explanations by statistically disentangling the direct effect of sexual debut on substance use from general age trends and stable propensities for risky behavior.

In the end, we found some support for all three explanations. As expected, the youth in our study became more sexually active and used more substances as they got older. Furthermore, some youth were more sexually active than others, initiated sexual activity earlier, and consistently used more substances across time (even before they became sexually active). Yet even after accounting for these general trends, sexual debut still predicted an increase in substance use. In other words, the act of sexual debut itself seems to entail some additional risk above and beyond a youth’s general propensity to engage in problem behaviors.

It is important to note that the direct effect of sexual debut on substance use was small. The majority of the association between sexual debut and substance use came down to the fact that both behaviors increased over time and that some youth were simply more likely to become sexually active and use substances (with no direct link between these behaviors).

So, returning to the opening question: does having sex for the first time make teenagers more likely to use drugs? The answer seems to be a qualified yes, with the caveat that other factors have a more powerful influence on which youth use drugs.

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