Several GWAS studies have evaluated opioid use disorder (OUD) and/or opioid dependence, and have identified a variety of loci including SNPs linked to OPRM1, KCNG2, CNIH3, LOC647946, LOC101927293, CREB1, PIK3C3, and RGMA52–57 Additional human linkage studies have identified sex-specific traits58, epigenetic biomarkers59 or copy number variations60 for risk of OUD. Here, OPRM1 is linked to opioid use disorder.