Background: The impact of prescription opiate (PO) misuse on the incidence of initiation into injection drug use among youth has not been well characterized. This study longitudinally examined non-injection PO misuse and time to injection initiation among street-involved youth.

Methods: Data were derived from a prospective cohort of street-involved youth from September 2005 to May 2014. An extended Cox model with time-dependent variables was used to examine the relationship between a history of non-injection PO misuse at baseline and time to injection initiation.

Results: At baseline, among 462 injection naïve youth who completed at least one study follow-up to assess for injection initiation, 178 (39%) participants reported having ever misused a PO via non-injection. During study follow-up, 97 (21%) injection initiation events were observed. In multivariable Cox regression analysis, a baseline history of PO misuse was independently associated with time to injection initiation (adjusted relative hazards [ARH] = 1.70, 95% CI: 1.12-2.58) after adjustment for time-updated potential confounders. In sub analysis, dilaudid was the category of PO that was most highly associated with injection initiation (AHR = 1.94, 95% CI: 1.03-3.63).

Conclusion: Among a sample of high-risk youth, PO misuse independently predicted injection initiation. These findings underscore the urgent need for interventions to prevent and treat PO use among youth, as a means of preventing initiation of injecting.