Patients with opioid dependence and carrying the CYP2D6*1 allele in addition to an increased function allele may have a decreased response to methadone maintenance therapy (MMT) as compared to patients carrying two normal function alleles or two no function alleles. However, conflicting evidence has been reported. This drug-variant pair has been assigned a 鈥渘o recommendation鈥?by CPIC, as it was determined to be not clinically actionable. Other genetic and clinical factors may also affect response to MMT.