The role of impulsivity in injection-related risk behaviours among people who inject drugs in Montreal, Canada

Background: Impulsivity is a key contributor to substance use disorder, with previous research consistently demonstrating its role in the initiation, continuation and severity of drug use. Less is known about its association with injection-related risk behaviours, including injection equipment sharing and public injection, important drivers of HCV and HIV epidemics among people who inject drugs (PWID). Methods: Data were drawn from HEPCO, an ongoing community-based cohort study of PWID in Montreal, Canada. We used the first observation from participants who reported injecting drugs in the past three months and were administered the Cambridge Neuropsychological Test Automated Battery (CANTAB) (August 2017–March 2020). The Stop Signal Task was administered to measure “response inhibition,” i.e., an individual's ability to inhibit a prepotent or automatic response when presented with a stop signal or cue. Stop-signal reaction time (range: 50–1000 ms) was analyzed as a continuous indicator of impulsivity. Univariate and multivariable logistic regression were utilized to estimate associations between impulsivity and i) sharing injection equipment and ii) injection in public places, and identify other correlates of the study outcomes. Results: Of 156 PWID included in the study, 26 (17%) and 42 (27%) reported sharing injection equipment and injecting in public, respectively. The majority of participants were men (85%) and the mean age was 45 years. In multivariable analysis, impulsivity was significantly associated with injecting in public places (aOR = 1.26 per each 100-unit increase, 95% CI = 1.01, 1.60). Other correlates of injecting in public were: age (0.93 [0.88, 0.97] and unstable housing (3.51 [1.43, 8.61]). There was no evidence for an association between impulsivity and injection equipment sharing (0.85 [0.65, 1.10]). Conclusion: This study underscores the importance of impulsivity in public injection, a behaviour strongly associated with HIV and HCV transmission among PWID. These findings highlight the need for public health interventions that both mitigate impulsivity, such as behavioural or pharmacological therapies, and accommodate it through expanding low-threshold harm-reduction services, including access to supervised consumption sites and sterile injecting equipment.