Does substance use disorder treatment completion reduce the risk of treatment readmission in Chile?

Background: Recovery from substance use disorders (SUD) often entails multiple treatment episodes, which clashes with a context of a treatment system with limited resources and long waiting. Treatment retention and completion have been pointed out as key elements for sustainable achievement; however, most of the evidence generated focuses on opioids and injected substances, which is hardly transferable to the Latin American context.Objectives: This study aims to estimate the effect of SUD treatment completion on the risk of being readmitted to a SUD treatment in Chile.Methods: We conducted a retrospective analysis on a database of 107,559 treatment episodes from 85,048 adult patients admitted to SUD treatment during 2010-2019 in Chile. We adjusted two separate Prentice Williams and Petersen Gap Time models, to explore the association between treatment completion (vs. non-completion) and up to the third treatment readmission among residential and ambulatory modalities while controlling for time-varying covariates. To examine whether the effect of treatment completion differs between events, we included an interaction term with the stratification variable.Results: We found that completing the treatment cuts readmission risk for the first event by 17% (Average Hazard Ratio [95% CI] = 0.83 [0.78, 0.88]) and by 14% for the second entry (Average Hazard Ratio [95% CI] = 0.86 [0.78, 0.94]) in ambulatory treatments. We did not find evidence that completing a treatment reduces the readmission risk for residential treatments or third attempts in ambulatory ones. Conclusion: Treatment completion was associated with benefits in cutting readmission risk for the first and second episodes in ambulatory treatments among Chilean adults. It is important to explore different mechanisms than treatment retention for residential treatments.