No evidence of association between 118A>G OPRM1 polymorphism and heroin dependence in a large Bulgarian case-control sample.

The μ-opioid receptor is the primary site of action of most opioids. The 118A>G (rs1799971) polymorphism in exon 1 of the μ-opioid receptor gene (OPRM1) leads to an Asn40Asp amino acid change that affects a putative N-glycosylation site. It has been widely investigated for association with alcohol and drug dependence and pain sensitivity, with mixed results.