Oral Naltrexone Treatment Participants were required to complete opiate detoxification before being invited to attend the therapeutic workplace for induction onto oral naltrexone (Depade®; Mallinckrodt Inc.). All opiate detoxification and naltrexone inductions were overseen by a physician and were guided solely by clinical considerations. All participants were notified of the potential for heightened risk of overdose in relation to naltrexone treatment and after extended periods of opiate abstinence. These notifications were issued by study staff during the study consent process, and at monthly assessments, and were issued by medical staff prior to initiating naltrexone treatment, and whenever a blood draw was conducted. Overdose risk reminders were read aloud and signed by the study participants. Finally, monthly lunch-time overdose prevention seminars were provided and free pizza was provided to encourage seminar attendance.