Transition Trajectories of Youth Substance Use Across Alcohol, Tobacco, and Other Illicit Drugs

Overview: The longitudinal study based on national data examined adolescents’ use of initial drug classes (i.e., tobacco, alcohol, and illicit drugs) and how the initiation leads to the use of other substance classes. We also explored the most common use statuses and sequences across these substance classes after the initiation.Proposal text: Background
Adolescent substance use has been prevalent. In 2019, 28.6% of adolescents 12 to 17 years old used a substance in the past year, with the proportion of using tobacco, alcohol, and illicit drugs accounting for 8.3%, 21.2%, and 17.2%, respectively (Center for Behavioral Health Statistics and Quality, 2020). Substance use initiation and progression across tobacco, alcohol, and illicit drugs have been a critical research focus in understanding substance use patterns (Goodwin et al., 2018; Keyes et al., 2019; Mathers et al., 2006; Patton et al., 2005). However, the lack of appropriate lifetime substance use history data has limited investigations in the area.
Methods
We used 2015 to 2019 pooled data (n = 18,861) from the National Survey on Drug Use and Health (NSDUH) to examine adolescents' (14 to 17 years old) drug use initiation and progression. We first created substance use sequence data based on adolescents’ ages of initiating each substance to turn the cross-sectional data into longitudinal data. We then examined adolescents’ substance classes (i.e., tobacco, alcohol, and illicit drugs) in their first substance use, and applied the Life Table method to depict the trajectories from the initial classes to another class over time. Additionally, we explored the most common use statuses and sequences across tobacco, alcohol, and illicit drugs after adolescents initiated substance use. Finally, we used Cox regression models to partial out confounding factors in the examined associations.

Results
Nearly half of the adolescents (48.94%) initiated substance use with alcohol, 18.34% with tobacco, and one third (32.72%) with other illicit drugs. Overall, one year after substance use initiation, adolescents had a 15% to 30% probability of transitioning to another class of substance, and the rates increased to about 80% to 90% by year 8. Findings from the Cox regression models show that compared with adolescents who initiated with alcohol, adolescents who initiated with tobacco (HR = 1.49, p < 0.01) and other illicit drugs (HR = 1.19, p < 0.01) were more likely to transition to another substance class.
Implications
Adolescents’ substance use onsets, regardless of drug classes, are significantly associated with transitioning to using other substances, and the likelihood is the highest in the first several years after the initiation. Given the harm of adolescent substance use and the rapid transition to other substances, it is important to develop prevention programs that target all substance classes as well as intervention programs that can promptly respond to youth substance use initiations to interrupt its progression toward the use of other substances.