Hooked before the first injection: The role of prescription opioids in early injection drug use initiation in San Francisco.

Background: Injection drug use (IDU) is a major public health concern linked to HIV and hepatitis C infections, overdose deaths, and other adverse health and social welfare outcomes. We examined the role of self-reported painkiller dependence in shaping the timing and progression of IDU initiation. Methods: Data are from the National HIV Behavioral Surveillance (NHBS) survey conducted in San Francisco in 2022. Cumulative IDU initiation patterns were analyzed, stratified by prior painkiller dependence and other background characteristics using survival analysis. The chi-square was used to examine differences in age at first injection and related characteristics. Results: Of 519 people who inject drugs (PWID) surveyed, 23.3% reported initiating IDU before the age of 18 years and 35.3% reported being hooked on painkillers before initiating IDU. Early IDU initiation was also associated with bisexual sexual orientation, lower educational attainment, younger age, and starting injection before 1990. Participants hooked on painkillers showed earlier and faster progression to injection drug use, with 50% initiating by age 40 compared to after age 50 among those not previously hooked (P < 0.001). By race/ethnicity, divergence in age at initiating IDU was evident after the late 20s and early 30s, with Black PWID having a later and slower onset of IDU compared to other groups (P < 0.001). Conclusions: We found a strong continuing association between prior self-reported painkiller dependence and earlier progression to IDU. These findings underscore the critical need for comprehensive public health interventions that address the root causes of opioid misuse and effectively target the transitions contributing to IDU.