Unsupervised injectable opioid agonist therapy (iOAT) may decrease the unmet treatment needs for people who inject opioids. We aimed to model whether unsupervised iOAT may be effective in reducing fatal and non-fatal overdose, and estimate the cost per life saved.

The study used a decision tree model based on Australian and international parameters for overdose risk in people who inject opioids who are: not on OAT; new/stable to methadone/buprenorphine treatment; on iOAT; or on unsupervised iOAT. We modeled scenarios of (1) current OAT only (status quo), or current OAT plus either (2) 5% supervised iOAT, (3) 5% supervised or 5.69% unsupervised iOAT (based on willingness to enroll), OR (4) 1.2% supervised and 10% unsupervised iOAT (the same cost as scenario 2). The study measured overdoses (fatal and nonfatal) and treatment costs per 10,000 people who inject opioids per annum, and cost-per deaths averted on implementation of iOAT.

With current OAT, the study found an estimated 1655.5 (1552.7-1705.3) overdoses, 19.3 (17.9-20.3) overdose deaths and AUD 23,335,081 in treatment costs per 10,000 people per annum. Implementation of 5% enrollment in supervised iOAT costs an additional AUD 14,807,855 and showed a reduction of 122.9 (95% UI 114.2-130.5) overdoses and 2.0 (1.8-2.0) overdose deaths per 10,000 people per annum ($7,774,172 [7,283,182-8,146,989] per death averted). For the same treatment costs, additional coverage of 10% unsupervised iOAT and 1.2% supervised iOAT could be achieved, which the study estimated to prevent 269.0 (95% UI 250.0-278.7) overdoses and 4.0 (3.7-4.2) overdose deaths per 10,000 people per annum ($3,723,340 (3,385,878-3,894,379) per death averted), alongside further benefits of treatment unaccounted for in this study.

An implementation scenario with greater unsupervised iOAT compared to supervised iOAT allows for an increased reduction in overdose and overdose deaths per annum at the same cost, with the additional benefit of increased treatment coverage among people who inject opioids.