with the A/G and G/G genotypes also have decreased pupillary constriction compared to A/A individuals in response to treatment with levomethadone, a methadone-like agonist [69]. This differential response is consistent with the hypothesis that the G allele of A118G may result in reduced analgesia after treatment with opioid medications. The minor alleles of an additional 12 SNPs are associated with insomnia and reduced libido in methadone maintenance patients [70]. Despite the logical connection between OPRM1 and opioid dependence, it is difficult to identify any firm pharmacogenetic connections between OPRM1 polymorphisms and treatment for opioid dependence with the limited number of studies available. Additional studies that examine treatment efficacy are clearly needed. Further pharmacogenetic analyses of specific ethnic groups may also be beneficial due to the potential ethnic differences in the association of the A118G polymorphism with opioid dependence.
