Introduction: Recent research has begun to explore the transition from nonmedical use of prescription opioids (POs) to heroin and injection drug use, adding to earlier literature identifying factors that influence the transition from intranasal to injection use of heroin. However, little research has explored how these transitions are embedded within young people's broader opioid use trajectories - individual pathways that may also include experiences of nonfatal overdose and drug treatment.
Methods: Data are from a study of 539 18-29 year-old New York City residents, recruited via Respondent-Driven Sampling, who reported past-month nonmedical use of POs and/or heroin use. Participants completed structured, computer-assisted interviews that included assessment of their ages at a series of "benchmark" events and experiences, including first use of a drug or route of administration, the onset of "regular" use of a drug (i.e., 1 or more times a week for at least 1 month), first overdose and first drug treatment.
Results: Results suggest a predictable, ordered pathway by which opioid use tends to progress in this cohort of young adults. Participants initiated nonmedical PO use at age 16.8, on average, and most transitioned to heroin use (83%) and heroin injection (64%), generally within 4 years of first PO misuse. Drug treatment was not typically accessed until after participants had progressed to heroin use. First overdose occurred Conclusions: Findings may help inform the optimal timing for delivery of primary, secondary and tertiary prevention efforts targeting young opioid users.

Highlights:
Youth began PO misuse at age 16.8 on average; 86% progressed to regular PO misuse.
92% of opioid-using youth had also misused benzodiazepines; 56% did so regularly.
Most PO users transitioned to regular heroin use (79%) and heroin injection (64%).
Regular heroin use and heroin injection began about 3.5 years after first PO misuse.
First OD occurred at the mean age of 20.2,