The current study provides support for the influence of the interactive effects of DAT1 and OPRM1 genes on subjective effects and patterns of alcohol consumption. Novel findings were the epistatic interactions between OPRM1*G and DAT1 A9 alleles on alcohol drinking frequency and negative subjective effects of alcohol. The current findings do not, however, provide any evidence of interactive effects of OPRM1 and DAT1 genotypes on the stimulant or positive subjective effects of alcohol in social drinkers. If replicated in a larger sample, these data suggest a modest protective effect of the OPRM1 gene in epistatic interaction with the DAT1 gene. These findings also may help explain some of the variability in results observed in prior studies of the OPRM1 A118G polymorphism. In conclusion, these findings highlight the biological importance of interactions between these two genes, and by extension interactions between brain opioid and dopamine systems in modulating individual differences in alcohol response.
