Kelley-Quon LI, Cho J, Strong DR, et al. - Researchers investigated if nonmedical prescription opioid use is correlated with subsequent initiation of heroin use in adolescents via performing an 8-wave prospective longitudinal cohort study involving high school students aged 14-15 years (n = 3,298) in Los Angeles, CA, who had never consumed heroin at baseline. They found that the mean per-wave prevalence of prior nonmedical prescription opioid use was 1.9%, and of current nonmedical prescription opioid use, 2.7%, from waves 1-7. In total, 70 students started heroin use during waves 2-8. Prior vs no and current vs no nonmedical prescription opioid use was positively linked to the initiation of subsequent heroin use. The estimated cumulative probabilities of ensuing heroin use initiation by wave 8 were 1.7%, 10.7%, and 13.1% for no, prior, and current nonmedical prescription opioid use statuses at waves 1-7, respectively. Correlations were attenuated in covariate-adjusted models but remained statistically important, and existing non-medical prescription opioid use risk estimates were stronger than associations of nonopioid use with subsequent initiation of heroin use. In all, among Los Angeles youth, nonmedical prescription opioid use was prospectively linked to subsequent heroin use initiation throughout 4 years of adolescence.