In another study by Lawford et al. [63], the frequency of the rs1800497 A1 allele in 95 Caucasian opioid-dependent patients was 19.0% compared to 4.6% in controls who had no history of alcohol or drug abuse (P=0.009). A follow up after one-year on an MMT program showed the A1 allele frequency to be 9.3% in the group with successful methadone treatment outcomes, and 22.7% in the poor treatment group (χ2=20.3, p<0.0001) [63]. It was concluded that less successful outcomes of MMT are associated with the A1 variant [63].
