Differences in heroin overdose risk associated with the unregulated drug market: Insights from a supervised injecting facility in Melbourne, Australia.

Abstract

Aims: To determine the contribution that variation in the unregulated drug market has on the risk of heroin overdose across individuals with different levels of personal overdose risk.

Design: A retrospective cohort study of heroin injecting episodes and overdose cases were examined over a 12-month period between 30 June 2022 and 30 June 2023.

Setting: The Medically Supervised Injecting Room in Melbourne, Australia.

Cases: 1474 witnessed heroin overdose cases were examined amongst a cohort of 337 individuals who were predominantly male (n = 276, 81.7%) with a median age of 43.5 years (interquartile range 37.25-49.00 years, range 20-75 years).

Measurements: The daily overdose rate was used to differentiate High and Low daily overdose risk categories. The number of overdose events that an individual experienced during the study period was used to differentiate people into Standard, Moderate and High personal overdose risk categories. Each overdose case was differentiated by the personal overdose risk of the individual who experienced the overdose, as well as the overdose risk of the day that overdose occurred. A stratified overdose risk profile was then derived across the nine different daily overdose risk and personal overdose risk categories.

Findings: The rate of overdose approximately doubled on High overdose risk days compared with Standard overdose risk days, increasing by a factor of 2.11, 2.41 and 2.03 times for individuals in the Standard, Moderate and High personal overdose risk groups. Conversely, the rate of overdose was also substantially reduced on Low overdose risk days to a factor of 0.17, 0.28 and 0.20, respectively.

Conclusion: Among heroin users in Melbourne, Australia, there is an approximately 10-times difference in the risk of overdose on some days compared with others, which appears to be attributable to the effects of the unregulated drug market and not the effects of variation in personal overdose risk of individuals.