Patients carrying the CYP2D6*1xN allele in combination with a normal function allele may have decreased concentrations of methadone as compared to patients carrying two normal function alleles or a normal function allele in combination with a no function allele. However, conflicting evidence has been reported. This annotation only covers the pharmacokinetic relationship between CYP2D6 and methadone and does not include evidence about clinical outcomes. 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 methadone concentrations.