Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence. It is marketed in generic form as its hydrochloride salt, naltrexone hydrochloride, and marketed under the trade names Revia and Depade. Naltrexone and its active metabolite 6-β-naltrexol are competitive antagonists at μ- and kappa-opioid receptors, and to a lesser extent at delta-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. Its use in alcohol (ethanol) dependence has been studied and has been shown to be effective. Naltrexone is metabolized mainly to 6β-naltrexol by the liver enzyme dihydrodiol dehydrogenase. Other metabolites include 2-hydroxy-3-methoxy-6β-naltrexol and 2-hydroxy-3-methoxy-naltrexone. These are then further metabolized by conjugation with glucuronide.