Analysis for OPRD1 receptor tSNPs revealed that of the five tSNPs tested, one marker (OPRD1^4, rs4654327) reached corrected p-value significance in the model assessing stimulation scores. Specifically, there was a significant effect of OPRD1^4 genotype on stimulation (β = 0.96, SE = 0.31, t = 3.07, p < .01), an effect of medication (β = 0.46, SE = 0.231, t = 2.0, p < 0.05), and a significant OPRD1^4 × medication interaction (β = −0.99, SE = 0.222, t = −4.46, p < .0001). This model also showed a significant effect of BrAC (β = 0.70, SE = 0.09, t = 7.69, p < .0001) and a trend-level BrAC × medication interaction (β = −0.15, SE = 0.087, t = −1.74, p = 0.08). As shown in Figure 3, the pharmacogenetic effect was such that carriers of the A allele at this locus reported greater naltrexone-induced blunting of alcohol stimulation. Controlling for OPRM1 genotype and removing non-Whites from analysis did not alter the significance of the medication × OPRD1^4 interaction.
