Alcohol increases the release of the endogenous (produced by the body) opioids beta-endorphin and enkephalin in animals and humans. Blocking opioid receptors in the brain with naltrexone leads to less alcohol-induced pleasure, high and intoxication and ultimately less craving and relapse for alchoholics. However, not all individuals with alcohol dependence respond to naltrexone. A team of researchers in the U.S. looked at the effects of a pair of genes called Asp40 and Asn40 on the effectiveness of naltrexone for the treatment of alcoholism. People can have either two Asp40 genes, two Asn40 genes or one of each. The researchers studied 604 alcoholics and found that those with the Asp40/Asp40 combination showed an increased percentage of days abstinent and a decreased percentage of heavy drinking days when treated with naltrexone rather than a placebo. However, those with ths Asn40/Asn40 combination fared no better on naltrexone than on a placebo.
Anton, Raymond F. ... [et al] - An evaluation of u-Opioid receptor (OPRM1) as a predictor of naltrexone response in the treatment of alcohol dependence: results from the Combined Pharmacotherapies and Behavioral Interventions for Alcohol Dependence (COMBINE) study Archives of General Psychiatry February 2008, 65(2), 135-144