Characteristics Associated with Nonmedical Methadone Use among People Who Inject Drugs in California

Background: Illicit, nonmedical use of opioid agonist medications such as methadone is an ongoing concern. Yet, few studies have examined nonmedical use of methadone by people who inject drugs (PWID). Objectives: This study describes the prevalence of nonmedical methadone use in a community sample of PWID and examines factors associated with recent use of nonmedical methadone. Methods: A cross-sectional sample of PWID (N?=?777) was recruited using targeted sampling and interviewed in California (2011?2013). Descriptive, bivariate, and multivariate logistic regression analyses were used to determine characteristics associated with nonmedical methadone use in the last 30?days. To determine if nonmedical methadone use was associated with overdose in the last 6 months, a separate multivariate analysis was conducted. Results: Among PWID sampled, 21% reported nonmedical methadone use in the last 30 days. In multivariate logistic regression analysis, nonmedical methadone use was associated with recent methadone maintenance treatment (adjusted odds ratio [AOR]?=?2.86; 95% confidence interval [CI]?=?1.90, 4.30), recent nonmedical buprenorphine use (AOR = 3.12; 95% CI = 1.31, 7.47), higher injection frequency (referent <30 injections; 30?89 injections AOR = 1.89; 95% CI = 1.19, 3.02; 90-plus injections AOR = 2.43; 95% CI = 1.53, 3.87), schizophrenia diagnosis (AOR = 2.36; 95% CI = 1.36, 4.10), recent non-injection opioid prescription use (AOR = 2.97; 95% CI = 1.99, 4.43), and recent injection opioid prescription misuse (AOR = 2.13; 95% CI = 1.27, 3.59). Nonmedical methadone use was found not to be associated with nonfatal overdose (AOR = 0.77; 95% CI = 0.38, 1.56). Conclusion: Nonmedical methadone use identifies a vulnerable subpopulation among PWID, is not associated with elevated nonfatal overdose risk, and evidences a need to expand methadone treatment availability.