The hydrochloride salt of naltrexone, a noroxymorphone derivative with competitive opioid antagonistic activity. Naltrexone and its metabolite 6-beta-naltrexol reverse the effects of opioids by binding to various opioid receptors in the central nervous system CNS), including the mu-, kappa- and gamma-opioid receptors; opioid effects of analgesia, euphoria, sedation, respiratory depression, miosis, bradycardia, and physical dependence are inhibited. Naltrexone is longer-acting and more potent compared to naloxone.