Differences in polysubstance use patterns and drug-related outcomes between people who inject drugs receiving and not receiving opioid substitution therapies

Aims: To test if polysubstance use profiles and drug-related outcomes differ between those receiving and not receiving opioid substitution therapies (OST) among people who inject drugs (PWID). Design: An annual cross-sectional, sentinel sample of PWID across Australia. Setting: Data came from 3 years (2011–13) of the Illicit Drug Reporting System (IDRS). Participants: A total of 2673 participants who injected drugs from the combined national IDRS samples of 2011 (n\ua0=\ua0868), 2012 (n\ua0=\ua0922) and 2013 (n\ua0=\ua0883). Measurements: Latent class analysis (LCA) was used to summarize participants' self-reported use of 18 types of substances, with the resulting polysubstance use profiles then associated with participant experience of a number of drug-related outcomes. Findings: Polysubstance use profiles exhibiting a broad range of substance use were generally at increased risk of negative drug-related outcomes, whether or not participants were receiving OST, including thrombosis among OST receivers [odds ratio (OR)\ua0=\ua02.13, 95% confidence intervals (CI)\ua0=\ua01.09–4.17], injecting with used needles among OST receivers and non-receivers, respectively (OR\ua0=\ua02.78, 95% CI\ua0=\ua01.50–5.13; OR\ua0=\ua02.15, 95% CI\ua0=\ua01.34–3.45) and violent criminal offences among OST receivers and non-receivers, respectively (OR =2.30, 95% CI\ua0=\ua01.16–4.58; OR\ua0=\ua01.87, 95% CI\ua0=\ua01.14–3.07). An important exception was non-fatal overdose which was related specifically to a class of PWID who were not receiving OST and used morphine frequently (OR\ua0=\ua01.83, 95% CI\ua0=\ua01.06–3.17). Conclusion: Regardless of opioid substitution therapies usage, people who inject drugs who use a broad-range of substances experience greater levels of injecting-related injuries and poorer health outcomes and are more likely to engage in criminal activity than other groups of people who inject drugs