Several studies report the effect of the OPRM1 118A>G polymorphism on the HPA axis. The 118G allele was associated with a robust cortisol response to naloxone blockade in subjects of predominantly European ancestry (Chong et al. 2006; Hernandez-Avila et al. 2003; Wand et al. 2002), but the effect was not found in Asians (Hernandez-Avila et al. 2007). It was also associated with blunted cortisol response to psychosocial stress (Chong et al. 2006) and with greater baseline concentrations of plasma cortisol in healthy subjects (Bart et al. 2006; Hernandez-Avila et al. 2007).
