A series of meta-analyses performed on 55 studies has shown an association between the DRD2 A1 allele and SUD in Caucasian and non-Caucasian groups [16]. However, in the particular case of opioid use disorders, associations with the A1 allele have been found in some studies [17,18], but not in others [19,20]. The aim of the present study was to examine the association of heroin dependence with DRD2 A1 alleles in Spanish subjects of European origin.
