It is important to highlight that with regard to OPRM1, existing studies have generally not found a significant association with substance use disorder diagnoses (Arias et al., 2006). However, a functional single nucleotide polymorphism of the OPRM1 gene may predict response to naltrexone, an opiate antagonist that has actions at mu opiate receptors. Specifically, carriers of the OPRM1 +118G allele have been found to respond better to naltrexone therapy for alcohol dependence relative to homozygotes for the OPRM1 +118A allele (Anton et al., 2008; Oslin et al, 2003); although not all studies support this finding (e.g., Gelernter et al., 2007).
