Results from a one-year extension of a six-month pivotal study showed sustained efficacy of Vivitrol (once a month naltrexone), from Alkermes Inc, as measured by the number of Opioid-free urine screens in patients who received Vivitrol in combination with psychosocial treatment. At the onset, 114 patients from the six-month pivotal trial continued into the open-label, 52-week extension. Of these, sixty-seven patients continued treatment with Vivitrol, while 47 patients who had been on placebo crossed over to receive Vivitrol. Improvements observed in patients treated with Vivitrol during the six-month pivotal trial were maintained for the duration of the extension. Half of the patients (49%) who entered the extension study were completely abstinent for the duration, based on opioid-free urine screens. The extension study also measured opioid craving, improvements in quality of life measures, self-reported opioid use and incidence of physical Opioid Dependence, confirming the findings documented in the first pivotal study. Treatment with Vivitrol showed a low rate of clinical adverse events, the absence of severe adverse events and a low overall rate (2.6%) of injection site pain. Overall, nearly 65% of patients completed the open-label study, representing a high completion rate for an addiction study.