CAMBRIDGE, Mass.--(BUSINESS WIRE)--Alkermes (Nasdaq: ALKS) today announced positive results from a Phase 2 exploratory study of injectable extended-release naltrexone (XR-NTX) in opioid-using adults not physically dependent on opioids, which showed that the two highest doses tested demonstrated opioid blockade for 28 days. The clinical data from this study will be used to support the further development of XR-NTX for the treatment of opioid dependence, a serious chronic brain disease. This pilot study was conducted at the Johns Hopkins University School of Medicine and the National Institute on Drug Abuse (NIDA), two leading institutions in the treatment of addiction.