Alcohol is the second most commonly used drug of abuse worldwide, nicotine being the most common. More than 16 million people were abusing or dependent on alcohol in 2011 in the United States alone, creating a substantial societal burden (National Survey on Drug Use and Health, http://www.drugabuse.gov). Evidence suggests that the rewarding effects and positive reinforcement experienced after alcohol use are regulated by opioid receptors, with alcohol causing the release of endogenous opioids in the brain and indirectly activating the opioid signaling pathways [81, 82]. Like nicotine, the regulation of the effects of alcohol by the opioid system has led to substantial research on the role of OPRM1 polymorphisms in alcoholism treatment and risk.
