In this study, we have extended our earlier work in Caucasians (Nielsen et al. 2009) by examining in subjects of two ethnicities, African-Americans and Hispanics, methylation levels at 16 CpG sites in the OPRM1 promoter region. Subjects were former severe heroin addicts stabilized in methadone maintenance pharmacotherapy and non-drug using controls. OPRM1 methylation levels of these subjects were compared to methylation levels in Caucasians that were recently reported (Nielsen et al. 2009).
