Abstract Background: Health-related quality of life (HRQOL) is widely used as an indicator of health status. However, few studies have examined predictors of HRQOL among injection drug users (IDUs). We investigated factors associated with HRQOL among IDUs in Taiwan. Methods: In this cross-sectional study, recruited IDUs completed an HRQOL-related interview at methadone clinics in Taipei during 2012e2013. Multiple linear regression was used to identify factors associated with HRQOL. Results: Of 802 eligible participants, 85.4% were male; mean (SD) age was 44.7 (8.7) years. Mean scores for physical, psychological, social, and environmental HRQOL were 13.2, 11.8, 12.5, and 12.5, respectively. In multivariate analysis, social support was significantly associated with better HRQOL in all domains (b ¼ 0.56, 0.87, 0.83, and 0.64, respectively), while obtaining most income from temporary jobs or other noncriminal sources was significantly associated with worse HRQOL in all domains (b ¼ À1.00, À1.03, À1.15, and À1.22, respectively). Receiving methadone treatment was associated with good physical and psychological HRQOL (b ¼ 1.47 and 0.79, respectively), while history of drug overdose (b ¼ À0.40 and À0.53, respectively), history of cutaneous abscess (b ¼ À0.45 and À0.53, respectively), and human immunodeficiency virus (HIV) positivity (b ¼ À0.41 and À0.58, respectively) were associated with lower physical and psychological HRQOL. Male sex (b ¼ À0.64 and À0.70, respectively) and a greater number of incarcerations (b ¼ À0.11 and À0.12, respectively) were associated with poor social and environmental HRQOL. Conclusion: Poor HRQOL was associated with a number of factors among IDUs at methadone clinics in Taipei, Taiwan. To improve HRQOL in this population, future programs should focus on IDUs with a history of drug overdose. In addition, methadone programs and social support should be integrated to improve HRQOL among this socially marginalized population
