While only exploratory, we did find that a naltrexone effect on natural drinking was predicted by an interaction of DAT VNTR with OPRM1 genotypes. Those with a least one DAT 9 VNTR who also had the asn40asn OPRM1 genotype had a lower alcohol intake while taking naltrexone. The same individuals (DAT 9 VNTR/OPRM1 asn40asn), who responded best to naltrexone, also had the highest stimulation to alcohol in the bar lab setting. While, in this study, we did not find an effect of naltrexone on this genetic interaction, in the past we have found that naltrexone actually broke the link between alcohol stimulation and further drinking (Anton et al., 2004). However, since the number of individuals in each DAT/OPRM1 group is small, especially when split by medication assignment, these results require cautious interpretation.
