the majority of the results pointing towards an association between the A118G polymorphism and alcohol dependence do not reach statistical significance and the few significant studies report conflicting results with respect to the ‘at-risk’ allele, the evidence regarding the link between OPRM1 polymorphism and alcohol dependence risk can be considered scarce. This being said, however, the A118G (Asn40Asp) polymorphism seems to moderate the hedonic, but not the sedative, effects of drinking alcohol, as alcohol-dependent patients carrying the G-allele have greater alcohol-induced stimulation, vigor and positive mood (Ray et al., 2013), as well as a stronger link between desire to drink in the evening and later night drinking (Kranzler et al., 2013). Moreover, as G-allele carriers tend to have attenuated cortisol responses under a range of stressful events (Pratt and Davidson, 2009; Schwandt et al., 2011), it might modify their vulnerability to alcohol use disorders, or to anxiety disorders, or to depressive disorders, or to some combination thereof, known to be clinically relevant and prevalent (Pirkola et al., 2005).
