BACKGROUND: Opioid use disorder (OUD) affects millions of individuals each year in the United States. Patient retention in medications for opioid use disorder (MOUD) treatment is suboptimal. This study examines and quantifies the associations between each additional month of buprenorphine or methadone use and nonprescribed opioid use. METHODS: Data were obtained from an 18-month longitudinal, observational cohort study of patients (age ≥ 18 years) treated for OUD. Patients completed a baseline self-reported questionnaire between March 2018 and December 2019 and were asked to complete follow-up questionnaires at approximately 3-, 6-, 12-, and 18-months post-baseline until May 2021. Patients treated with buprenorphine or methadone, without taking other MOUD at least 12 months prior to baseline, were included. Outcomes included past 30-day use of prescription opioids nonmedically, heroin, or illegally made fentanyl. A multivariable, multilevel regression model with a binomial distribution and a logit link was used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs). RESULTS: This study included 353 patients taking buprenorphine (mean [standard deviation, SD] age 39 [11] years
226 [64%] female), and 785 patients taking methadone (mean [SD] age 42 [12] years
392 [50%] female). Each additional month of MOUD treatment was associated with a 25% decrease in the odds of past 30-day nonprescribed opioid use for patients taking buprenorphine (aOR [95% CI] = 0.75 [0.68-0.83]), and a 17% decrease for patients taking methadone (aOR = 0.83 [0.79-0.87]). The COVID-19 pandemic (aOR = 9.29 [2.96-29.17]
aOR = 3.19 [1.74-5.86]) and MOUD adverse reaction experiences (aOR = 3.07 [1.11-8.48]
aOR = 2.51 [1.01-6.22]) were significantly associated with higher odds of nonprescribed opioid use among buprenorphine and methadone groups. CONCLUSION: Among patients treated with buprenorphine or methadone, with each additional treatment month since baseline, those who continued with treatment appeared to be more likely to report 17% to 25% decreased odds of past 30-day nonprescribed opioid use. Our findings can be used by clinicians in the shared decision-making process with patients, emphasizing the value of sustained retention in MOUD.