Background: In Sweden, individuals with severe substance use disorder may be committed to compulsory care under the Care of Abusers Act (LVM). Mortality after discharge from LVM is high, particularly from opioid-related causes. Until February 2016, participation in opioid agonist therapy (LARO) was prohibited during LVM care despite national treatment guidelines. A regulatory change on 15 February 2016 allowed initiation and continuation of LARO during compulsory care. This study aimed to assess the impact of that reform on LARO uptake and post-discharge mortality. Methods: Using linked national registers, we followed all individuals discharged from LVM between 2012 and 2019. Participation in LARO during LVM was identified through prescription data and in-facility medication records. Mortality within 180 days after discharge was analyzed using Cox regression. Analyses included before–after comparisons around the policy change with interaction by LARO eligibility, and direct comparisons between eligible clients who did versus did not participate in LARO during LVM. Results: After the policy change, the proportion of LVM episodes involving LARO increased from approximately 3%–4% in 2015 to over 15% by 2020. Mortality within 180 days after discharge declined after the reform, with a larger reduction among clients eligible for LARO. Among eligible clients admitted after the policy change, participation in LARO during LVM was associated with lower mortality (hazard ratio 0.15, 95% CI 0.04–0.59). Conclusions: Allowing opioid agonist therapy during compulsory care was associated with increased treatment uptake and reduced short-term post-discharge mortality. Integrating evidence-based treatment into compulsory care may reduce avoidable deaths.