The overarching aim of this trial is to evaluate naltrexone's efficacy in light of genetic variation and brain response to alcohol cues utilizing a neuroimaging paradigm. This trial has four specific aims. First, this trial will evaluate whether the presence of the OPRM1 Asp40 allele substitution is associated with improved treatment response to naltrexone in treatment-seeking alcoholics. Second, it will evaluate whether there is a difference in the naltrexone dampening of the alcohol cue-induced brain activation dependent on OPRM1 genotype. Third, it will explore whether alcohol cue-induced brain activation dampening by naltrexone might be a mediating factor in the treatment effects of naltrexone, the OPRM1 gene, or their interaction that might be observed in the first aim. Finally, this trial will evaluate the effect of medication compliance, or adverse effects, on the observed medication by genotype treatment response. A secondary aim will measure medication compliance and side effects based on OPRM1 genotype.