Association of Medication-Assisted Treatment and Age With Treatment Completion Among Veterans Seeking Non-VA Treatment for Opioid use Disorder at Non-Veterans Health Administration Facilities.

Background: Medication-assisted treatment has been shown to be effective in treating opioid use disorder among both older adults and veterans of U.S. Armed Forces. However, limited evidence exists on MAT's differential effect on treatment completion across age groups. This study aims to ascertain the role of MAT and age in treatment completion among veterans seeking treatment in non-Department of Veterans Affairs healthcare facilities for opioid use disorder.

Methods: We used the Treatment Episode Data Set-Discharges (TEDS-D; 2006-2017) to examine trends in treatment and MAT usage over time and TEDS-2017 to determine the role of age and MAT in treatment completion. We examined a subset of those who self-identified as veterans and who sought treatment for an opioid use disorder.

Results: Veterans presented in treatment more often as heroin users than prescription opioid users, and older veterans were more likely to get MAT than younger veterans. We found that before propensity score matching, MAT initially appeared to be associated with a lower likelihood of treatment completion in inpatient ($\beta $ = -1.47, 95% CI -1.56 to -1.39) and outpatient ($\beta $ = -1.40, 95% CI -2.21 to -0.58) settings, and age (50+ years) appeared to mediate the effect of MAT on treatment completion ($\beta $ = -0.54, 95% CI -0.87 to -0.21). After matching, older veterans were more likely to complete substance use disorder treatment ($\beta $ = 0.21, 95% CI 0.01-0.42), while age no longer mediated the effect of MAT, and MAT had a significant positive impact on treatment completion in detox settings ($\beta $ = 1.36, 95% CI 1.15-1.50) and inpatient settings ($\beta $ = 1.54, 95% CI 1.37 -1.71).

Conclusion: The results show that age plays an important role in outpatient treatment completion, while MAT plays an important role in inpatient treatment completion. Implications for veterans are discussed.