Low frequency genetic variants in the μ-opioid receptor (OPRM1) affect risk for addiction to heroin and cocaine

► We performed case-control analyses of low frequency genetic variants in OPRM1 in drug addicted individuals. ► 1377 European Americans and 1238 African Americans addicted to heroin or cocaine were genotyped for 4 SNPs in OPRM1. ► One SNP, rs rs62638690, was significantly associated with cocaine and/or heroin addiction in European Americans. ► Previous studies have found this SNP to reduce the potency of the μ-opioid receptor for opioids.