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 = 868), 2012 (n = 922) and 2013 (n = 883).

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) = 2.13, 95% confidence intervals (CI) = 1.09-4.17], injecting with used needles among OST receivers and non-receivers, respectively (OR = 2.78, 95% CI = 1.50-5.13; OR = 2.15, 95% CI = 1.34-3.45) and violent criminal offences among OST receivers and non-receivers, respectively (OR =2.30, 95% CI = 1.16-4.58; OR = 1.87, 95% CI = 1.14-3.07). 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 = 1.83, 95% CI = 1.06-3.17) 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.