The purpose of this open-label pilot study is to determine the tolerability and applicability of outpatient long-acting injectable naltrexone (Vivitrol) treatment in individuals age 16-25 ("older youth") with opioid use disorder. We aim to have 16 older youth complete this trial. Participants will undergo an outpatient detoxification / induction procedure that has been honed over the past 13 years of work with this medication by others in our Division and is currently being used safely in opioid-dependent adults in an ongoing clinical trial. The detoxification / induction procedure consists of a single day of buprenorphine followed by a washout day and 4 days of ascending oral naltrexone doses prior to administering a dose of injectable naltrexone, typically at Day 8. Participants will then receive an additional Vivitrol injection 4 weeks after the first; they will also receive weekly medication management therapy with a research psychiatrist. Following the 9 week trial, participants and are eligible for an additional third injection followed by up to 4 weeks of therapy while proper follow-up treatment is arranged.