BACKGROUND There are limited longitudinal data on national patterns of opioid agonist treatment (OAT). This study describes 10-year trends in the sales of OAT medicines in Australia.

METHODS A descriptive and time-series analysis of methadone, sublingual (SL) buprenorphine (+/-naloxone), and long-acting injectable (LAI) buprenorphine sold in Australia between 2013 and 2022 was performed. Total units sold were converted into an estimate of the number of clients that could be treated over a 28-day period with that amount of medicine ('client-months').

RESULTS Between January 2013 and December 2022, the estimated number of client-months on: any OAT increased by 50 % to 53,501, methadone decreased (-8.5%), SL buprenorphine increased (+78%), and LAI buprenorphine increased substantially after September 2019. In January 2013, 78 % of OAT client-months received methadone. By December 2022, 48 % received methadone, 26 % SL buprenorphine, and 26 % LAI buprenorphine. Between 2013 to 2022, OAT client-months per capita were highest in the state of New South Wales. Over the study period, greater increases in OAT were observed in very remote areas (88%) compared to major cities (53%). The number of client-months in non-community pharmacy settings remained stable from 2013 to 2019/20, before increasing markedly. The introduction of LAI buprenorphine was associated with an immediate, sustained increase of 1,636 OAT client-months, and further increases of 190 OAT client-months each month.

CONCLUSION Patterns of OAT have shifted over the last 10-years with buprenorphine (SL/LAI) now the most common OAT used in Australia. The introduction of LAI buprenorphine has expanded OAT access, particularly in non-community pharmacy settings, and in remote areas.