Opioiddependent patients carrying allele C in SNP rs2234918 are more likely to use a high maintenance dose of methadone (≥ 90 mg / day) than those without allele C with OR = 1.556 (95% CI: 1, 049 - 2, 309). Opioid-dependent patients carrying TT genotype in SNP rs2234918 are less likely to use a high maintenance dose of methadone (≥ 90 mg / day) than those without TT genotype with OR= 0, 643 (95% CI: 0, 433 - 0, 953).