Patients with opioid dependence and carrying the CYP2D6*6 allele in addition to another no function allele may have an increased response to methadone maintenance therapy (MMT) as compared to patients carrying a normal function allele in combination with a no function allele. 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.