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Altered Pathways: Drug Abuse and Age of Onset

May 1, 2006
by Nora D. Volkow, MD
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Research indicates how young people can benefit from early intervention

To the question of whether drug use early in life heightens the risk for substance abuse problems later on, we can answer an assured “yes.” What is less clear is why this happens. Clinicians who see patients with substance abuse problems are likely accustomed to sifting through layers to uncover other influencing factors, such as dysfunctional family relationships, mental illness, or negative peer associations. Identifying environmental or psychosocial stressors may, in fact, be the most obvious place to start with a patient who presents with substance abuse problems. Less obvious—and adding to the tangle of contributory factors—is the role of the brain itself, particularly a brain transformed by drugs.

Research supported by the Na-tional Institute on Drug Abuse (NIDA) has taught us that the brain continues to develop through adolescence and into early adulthood. We now know that age matters when it comes to substance abuse, and although we still don't know exactly how it matters, we suspect that the brain's inherent plasticity during this time has consequences related to age of first exposure, duration of use, and other temporal variables.

Adding genetic factors to the mix further increases causal complexity. Is early onset of drug use a genetic marker, for example, or a causal factor that increases risk for later abuse? In any case, because the transition from drug use to drug abuse and addiction typically occurs between adolescence and young adulthood, characterizing the factors underlying this developmental period is crucial to understanding the path to long-term substance abuse.

Research points the way

Innovative research is helping to shed light on the various ways in which drugs can change the course of brain development and behavior. Recent studies have delved into the role of the brain to see how exposure to drugs at different points along a developmental trajectory changes the brain and leaves individuals more vulnerable to later problems. This research is enhanced by the availability of new technologies and neuroimaging tools that allow us to study the human brain like never before, literally to see into the brains of people addicted to drugs and discover how drugs are affecting brain function. This capability, along with advances in genetics to identify genes of vulnerability or protection, will help tailor interventions that can have the greatest impact.

Longitudinal studies looking at physical, psychosocial, and environmental variables have identified risk factors such as having a parent who abused substances, higher levels of overactiveness, and deficits in social functioning. Current studies aim to elucidate further the risk factors during adolescence, including how peers and the frequency and content of parent-child communication about drug use influence behavior.

Other NIDA-supported research is investigating the development of substance use, abuse, and disorder, guided by a biopsychosocial model reflecting the complexity of factors involved: biological, sociocultural, parenting, peer, school, and cognitive-emotional, and how they all interact and transact across the developmental trajectory. Studies to identify developmental pathways and biological mechanisms of vulnerability to substance use will inform early intervention and prevention strategies, will provide insight into why teens engage in risk-taking behavior, and will ascertain who is more (or less) susceptible to drug abuse and to long-term negative consequences.

Other research under way is giving the brain the central role. We know that drug abuse affects brain circuitry, motivation, and judgment. Are these effects intensified when drugs are allowed into a still-developing brain? Likely so. Findings from NIDA-sponsored animal studies suggest differences in voluntary intake of and response to other drugs of abuse based on age of drug exposure, with behavioral observations potentially linked to related changes in the brain.

Similar findings are emerging from research in young people. One study found teen smokers to be especially vulnerable to the physiological effects of nicotine, indicating that smoking may be more addictive if it is initiated during adolescence and that it may heighten response to other addictive drugs. Current NIDA-supported research is looking at how chronic marijuana use during adolescence alters brain function, particularly intellectual functioning, hypothesizing increased vulnerability to cognition-related changes in light of the pronounced brain development that typically occurs during adolescence. Other research projects are studying the consequences of marijuana use on brain development to identify behavioral or cognitive “markers” for youths who progress from use to addiction. Ultimately, this research will help us to understand better why young people are particularly vulnerable to the consequences of drug abuse and how resulting brain changes may influence their overall development.

How should professionals respond?

What does this all mean to the clinician working on the front lines of substance abuse treatment, other than the fact that drug addiction is complicated? Knowing that drug abuse may not only indicate other problems (e.g., family conflict, mental health issues, etc.) but also can actually change the course of brain development and behavior gives clinicians more puzzle pieces to consider when determining potential interventions.