Association of recent initiation of nonmedical prescription opioid use and initiation of injection and heroin use in a national sample of drug users

Background: Health risks associated with initiation of heroin use and of drug injection present a worrisome public health problem, one which is exacerbated by an epidemic of nonmedical prescription opioid use. No large-scale US studies of the transition to heroin use or to injection have been conducted during the period corresponding to the increase in nonmedical prescription opioid use. We explored associations between recent initiation of nonmedical prescription opioid use and initiation of heroin and drug injection. Methods: Data from 2005-2009 (n=138,928) were analyzed from the Addiction Severity Index-Multimedia Version Connect®, a national surveillance database of in-treatment drug users. Product-specific drug use questions captured nonmedical use, route of administration and drug source. Initiates were past year incident users; comparison populations were drug users with no history of injection or heroin use. Multilevel logistic regression analyses considered individual- and ZIP-code level risk factors for initiation. Results: Past year initiation of heroin and injection was reported by 2859 (3.4%) and 3652 (4.8%) people, respectively. The most commonly reported drugs injected by initiators were heroin, cocaine, and prescription opioids, chiefly oxycodone ER, morphine, and hydromorphone products. Adjusted models detected a dose-response relationship between recent initiation of nonmedical use of none, one, or more than one prescription opioid and increased odds of initiation of injection and heroin use. Area-level poverty, minority population, and male unemployment were independently associated with initiation. Conclusions: Harm reducing interventions and effective early treatment options should be aimed at nonmedical prescription opioid users and at these pivotal transition points.