This is an observational, "ancillary study" intended to describe opioid use among opioid use disorder patients following their discharge into the community from inpatient detoxification and/or short-term residential treatment programs affiliated with parent study CTN-0051, which assessed the comparative effectiveness of extended release injectable naltrexone (XR-NTX, Vivitrol®), an opioid antagonist recently approved and indicated for the prevention of relapse to opioid dependence, versus buprenorphine-naloxone (BUP-NX, Suboxone®), a high affinity partial agonist indicated for maintenance treatment of opioid dependence, as pharmacotherapeutic aids to recovery.