Associations between mental illness and non-medical use of prescription opioids among a sample of people who use drugs in Australia and New Zealand

Non-medical use of prescription opioids (NUPO) is an increasing public health concern in Australia and New Zealand. In response to a lack of research on NUPO in this setting, we investigated the associations between NUPO, mental illnesses, and other substance use, using data from the 2019 Global Drug Survey (GDS). Strategies to reduce NUPO-related harm were also discussed. Socio-demographic characteristics, mental illnesses, NUPO, and other substance use among 2019 GDS respondents were examined. Logistic regression was used to identify factors associated with past year NUPO. Data from 2752 Australian and New Zealand respondents who used drugs were analysed. Pastyear use of heroin, benzodiazepines, cannabis (containing THC), and ecstasy were associated with a greater odds of NUPO, while bipolar disorder managed with medications was associated with a lower odds of NUPO. All other mental illnesses, including co-morbid mental illnesses, were not associated with NUPO after adjusting for potential confounders. Of respondents who reported NUPO and answered secondary questions, 38.8% obtained opioids from a friend or family member. This study provides a unique understanding of potential risk factors for NUPO among people who report mental illness and drug use in Australia and New Zealand, and establishes a basis for future research that is aimed at reducing NUPO-related harm.