Mechanism: Naltrexone blocks opioid receptors that are involved in the rewarding effects of drinking alcohol and the craving for alcohol. It’s available in two forms: oral (Depade®, ReVia®), with once daily dosing, and extended-release injectable (Vivitrol®), given as once monthly injections.

Efficacy: Oral naltrexone reduces relapse to heavy drinking, defined as 4 or more drinks per day for women and 5 or more for men. It cuts the relapse risk during the first 3 months by about 36% (about 28% of patients taking naltrexone relapse versus about 43% of those taking a placebo). Thus, it is especially helpful for curbing consumption in patients who have drinking “slips.” It is less effective in maintenance of abstinence. In the single study available when the 2007 update of the Guide was published, extended-release injectable naltrexone resulted in a 25% reduction in the proportion of heavy drinking days compared with a placebo, with a higher rate of response in males and those with lead-in abstinence.

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