Objective: To determine the efficacy and tolerability of a long-acting intramuscular formulation of Nalmefene (Nalmefene Consta 393.1 mg) for the treatment of opioid-dependent patients. Design, Setting, and Participants: A 12 weeks, open-label, randomised controlled trial conducted between June 2009-July 2011, at 14 Hospital-based drug clinics, in the 12 countries. Participants were 18 years or older, had Diagnostic and Statistical Manual of Mental Disorders-5 opioid use disorder. Of the 3200 individuals screened, 3000 (93.7%) adults were randomized 1500 participants to receive injections of Long-acting depot formulations ofNalmefene (Nalmefene Consta 393.1 mg) given intramuscularly once in 12 weeks and 1500participants to receive extended-release Naltrexone (Vivitrol 380 mg), administered intramuscularly every fourth week for 12 weeks. Main Outcomes and Measures: The primary endpoints (protocol) were: Confirmed Opioid abstinence (percentage i.e. the number of patients who achieved complete abstinence during week 12). Confirmed abstinence or “opioid-free” was defined as a negative urine drug test for opioids and no self-reported opioid use. Weeks 1 - 4 were omitted from this endpoint to allow for stabilization of abstinence. Secondary end points included a number of days in treatment, treatment retention and craving. The study also investigated, on 275 participants, degree and time course of mu-opioid receptor occupancy following single doses of Nalmefene extended-release injection (Nalmefene Consta 393.1 mg) as well as the plasma concentration of Nalmefene and Nalmefene-3-O-glucuronide. Safety was assessed by adverse event reporting. Results: Of 3000 participants, mean (SD) age was 27.1 (±4.8) years and 831 (27.7%) were women. 1500 individuals were randomized to receive injections of Long-acting depot %K Nalmefene Consta %K Long-Acting Depot Formulations of Nalmefene %K Opioid Dependence %K Long-Term Delivery %K PLGA Polymers %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=93675