This study will assess the comparative effectiveness of extended release injectable naltrexone (XR-NTX) versus buprenorphine-naloxone (BUP-NX) as pharmacotherapeutic aids to recovery amongst treatment-seeking heroin- and/or prescription opioid-dependent participants. The primary goal of the study is to estimate the difference, if one exists, between XR-NTX and BUP-NX in the distribution of the time to relapse during the 6-month trial.