There are medications available to help people who drink excessive amounts of alcohol reduce or stop their drinking. One such medication is the opioid antagonist naltrexone, which has been approved for treatment of alcohol dependence by the Food and Drug Administration. Although naltrexone can reduce alcohol craving and help promote recovery for some individuals, it does not work for everyone. Prior research suggested that nicotine use/smoking status and genetic differences were predictors of response to naltrexone. This study further investigated the impact of nicotine use/smoking status and variation in the mu opioid receptor gene (OPRM1), specifically, an A118G single nucleotide polymorphism (SNP, or DNA sequence variation), on the effects of naltrexone on a range of drinking outcomes.