Opioid substitution therapy (OST) is the gold standard of care for the management of opioid use disorder. OST is also known to reduce HIV risk behaviors among people who inject drugs (PWID) by reducing the frequency of injecting. Given that data suggest that PWID play a key role in initiating others into drug injecting through exposing others to injecting behaviors, our objective was to explore whether an association existed between OST enrollment and initiating others into injecting among PWID.
Preventing Injecting by Modifying Existing Responses (PRIMER; NIDA DP2-DA040256-01), is a multi-site cohort study assessing the impact of a range of socio-structural factors on the risk that PWID initiate others into injection. Preliminary results were drawn from a single participating cohort of PWID in San Diego ≥ 18 years old who reported injection drug use 6 months prior to baseline (STAHR-II; NIDA R01DA031074). PRIMER survey items were measured at 24-month follow up, and the outcome was defined as reporting ever initiating others into injecting; sustained OST enrollment was defined as being enrolled at 2 or more study visits (i.e., ≥1 year). Logistic regression modeling was used to identify associations.
Participants (N=360) were predominantly male (n=253, 71%), with a mean age of 47 (Interquartile Range [IQR]: 38-55), and a median of 24 years injecting (IQR: 13-35). Thirty-nine percent (n=139) of participants reported ever enrolling in OST and 19% (n=70) reported being enrolled in OST during the study period. Less than half of participants (n=135, 38%) reported ever initiating others into injecting. In multivariable models, males who reported sustained enrollment in OST had decreased odds of initiating others into injecting (Adjusted Odds Ratio [AOR]: 0.23, 95% Confidence Interval [CI]: 0.10-0.50; p<0.01). Additionally, each year increase in age was associated with decreased odds of initiating others (AOR: 0.94, 95% CI: 0.91-0.97; p<0.01), and a higher number of years injecting was independently associated with increased odds of initiating others into injecting (AOR: 1.03, 95% CI: 1.00-1.06, p=0.05).
OST may improve community health and reduce HIV risk behaviors by reducing the incidence of injection drug use initiation. While preliminary, this study highlights the need to further investigate whether OST may, along with reducing injection-related harms, also impact the risk that individuals initiate injection drug use.