Predictors of transition to heroin use among initially non-opioid dependent illicit pharmaceutical opioid users: A natural history study

Background: Increases in illicit pharmaceutical opioid (PO) use have been associated with risk for transition to heroin use. We identify predictors of transition to heroin use among young, illicit PO users with no history of opioid dependence or heroin use at baseline. Methods: Respondent-driven sampling recruited 383 participants; 362 returned for at least one biannual structured interview over 36 months. Cox regression was used to test for associations between lagged predictors and hazard of transition to heroin use. Potential predictors were based on those suggested in the literature. We also computed population attributable risk (PAR) and the rate of heroin transition. Results: Over 36 months, 27 (7.5%) participants initiated heroin use; all were white, and the rate of heroin initiation was 2.8% per year (95% CI = 1.9%-4.1%). Mean length of PO at first reported heroin use was 6.2 years (SD = 1.9). Lifetime PO dependence (AHR = 2.39, 95% CI = 1.07-5.48; PAR = 32%, 95% CI = -2% to 64%), early age of PO initiation (AHR = 3.08, 95%; CI = 1.26-7.47; PAR = 30%, 95% CI = 2%-59%), using illicit POs to get high but not to self-medicate a health problem (AHR = 4.83, 95% CI = 2.11-11.0; PAR = 38%, 95% CI = 12%-65%), and ever using PO non-orally most often (AHR = 6.57, 95% CI = 2.81-17.2; PAR = 63%, 95% CI = 31%-86%) were significant predictors. Conclusion: This is one of the first prospective studies to test observations from previous cross-sectional and retrospective research on the relationship between illicit PO use and heroin initiation among young, initially non-opioid dependent PO users. The results provide insights into targets for the design of urgently needed prevention interventions.