Revisiting the Association Between "Gateway Hypothesis" of Early Drug Use and Drug Use Progression: A Cohort Analysis...

Background and objective: Findings from observational studies indicate that early drug use is a strong predictor of further drug abuse. Because competing explanations abound in cross-sectional studies, causal interpretations from these investigations pose considerable challenge. We evaluated the relationship between early drug use and progression, while estimating modifying influences of adolescents' social contexts. Method: We applied a national longitudinal survey of 11,182 adolescents growing into adulthood over a 14-year period. The data provided a natural setting to evaluate the relationship between early drug use and drug use in three subsequent waves. We applied generalized estimating equation models to analyze these relationships. Results: Evidence showed over a relatively short period (approximately one year) early drug use was an independent predictor of illicit drugs in adolescence but not adulthood. The adjusted odds ratio for using substances in adulthood were marijuana (aOR, 1.33; 95% CI: 1.11-1.60), illicit drugs (aOR, 1.49; 95% CI: 1.04-2.12) and cocaine (aOR, 5.00; 95% CI: 2.75-9.10). Further, drug use was higher among older adolescence living in a neighborhood and reporting drug use as a big problem. In adulthood, neighborhood drug problems appear to have minimal influence on drug use escalation. Conclusion: The current findings call into question the causal interpretation of early drug use among adolescents as determinants of future drug escalation in adulthood. The overall impact of peer relationships on future drug escalation might depend on not only the extent of adolescent closeness to peers but also on continuity of friendship over time and other influencing social contexts.