Prevalence and correlates of intentional substance use to reduce illicit opioid use in a Canadian setting.

Background: While preliminary evidence has begun to document intentional use of one substance to reduce the use of another, the phenomenon of drug substitution among people who use illicit opioids remains understudied. Therefore, we sought to estimate the prevalence and correlates of intentional substance use to reduce illicit opioid use among persons who use drugs (PWUD). Methods: We analysed data from three prospective cohorts of PWUD in Vancouver, Canada, using multivariable generalized estimating equations (GEE). Results: Between June 2012 and June 2016, 1527 participants were recruited and contributed 4991 interviews. Of those, 336 (22%) illicit opioid-using participants self-reported substitution to reduce illicit opioid use at least once during study period contributing 467 (9.4%) interviews. Among those interviews, substances substituted for opioids were alcohol (15 participants, 3.2%), stimulants (235, 50.3%), cannabis (129, 27.6%), benzodiazepines (21, 4.5%), and others (20, 4.3%). In multivariable GEE model adjusted for socio-demographic factors, reporting substitution to reduce illicit opioid use was positively associated with greater likelihood of daily cannabis use (Adjusted Odds Ratio = 1.56, 95% Confidence Interval: 1.24-1.96]. Conclusions: While daily cannabis use was associated with reporting opioid substitution attempts, additional study is needed to examine potential of cannabis/cannabinoids to reduce illicit opioid use.