Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence. Naltrexone should not be confused with naloxone (which is used in emergency cases of opioid overdose) nor nalorphine. Using naloxone in place of naltrexone can cause acute opioid withdrawal symptoms; conversely, using naltrexone in place of naloxone in an overdose can lead to insufficient opioid antagonism and fail to reverse the overdose. Naltrexone and its active metabolite 6-β-naltrexol are competitive antagonists at μ- and κ-opioid receptors, and to a lesser extent at δ-opioid receptors. The plasma half-life of naltrexone is about 4 h, for 6-β-naltrexol 13 h. The blockade of opioid receptors is the basis behind its action in the management of opioid dependence—it reversibly blocks or attenuates the effects of opioids.
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