Deconstructing the 'cheque effect': Short-term changes in injection drug use after receiving income assistance, and associated factors.

BACKGROUND & AIMS Disbursement of income assistance has been temporally associated with intensified drug use and related harms (coined the 'cheque effect'). However, relationships to injection drug use (IDU) remain understudied. We examined short-term 'cheque effects' and associated factors among people who inject drugs (PWID). DESIGN Cross-sectional analysis nested within a cohort study. SETTING Montreal, Quebec, Canada. PARTICIPANTS PWID receiving income assistance, with no employment income. A total of 613 PWID (median age 41, 83% male) contributed 3269 observations from 2011-2017. MEASUREMENTS & METHODS At each cohort visit, an interviewer-administered questionnaire captured retrospective reports of injection-related behaviour during the 2-day periods (i) before and (ii) including/after receiving last month's income assistance payment (number of injections; drugs injected; any receptive syringe sharing). The relative likelihood (odds) and magnitude (rate) of an increase in injection frequency ('cheque effect') were estimated in relation to social and behavioural factors using logistic and negative binomial regression in a covariate-adjusted two-part model. FINDINGS Prevalence of IDU and syringe sharing were, respectively, 1.80 and 2.50 times higher in the days following versus preceding cheque receipt (p<0.001). Among persons with past-month IDU, most observations showed increased injection frequency (52%) or no change in injection frequency (44%). Likelihood of a 'cheque effect' was positively associated with cocaine injection (Odds Ratio=2.64 [95% CI: 2.04-3.41]), unstable housing (1.27 [1.03-1.57]), and receiving opioid agonist therapy (1.60 [1.27-2.00]) during the same month. Magnitude of the 'cheque effect' was positively associated with past-month cocaine injection (versus injection of other substances, Rate Ratio=1.80 [95% CI: 1.43-2.16]), unstable housing (1.20 [1.02-1.38]), and frequent injection (2.94 [2.43-3.44]), but inversely associated with opioid agonist therapy (0.82 [0.68-0.95]) and prescription opioid injection (0.79 [0.66-0.93]) CONCLUSION: Among people who inject drugs in Montreal, Canada, injection drug use and receptive syringe sharing appear to be more prevalent in the 2 days after versus before receiving income assistance. The odds and rate of individual-level increases in injection frequency appear to be positively associated with cocaine injection (versus injection of other substances) and unstable housing.