The N2/N2 (NcoI) genotype of DRD2 gene is shown to be a marker of resistance to opium addiction, the N1/N1 genotype being considered as a risk marker for the disorder. The N1 allele was associated with opium addiction in Russian patients aged 16 years and younger at drug using onset. In Tatars, an association was found between the N1 allele and a risk of opium addiction development over 16 years of age. The N2/N2 genotype proved to be a marker of resistance to opium addiction in Tatars over 16 years of age at drug using onset. No association was found between TaqI A DRD2 polymorphism and opium addiction in the Russians and the Tatars.