Patients carrying the CYP2D6*1 allele in combination with an increased 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. Patients carrying the *1 allele in combination with a normal function allele may have decreased concentrations of methadone as compared to patients carrying two no function alleles, but increased concentrations of methadone as compared to patients carrying a normal function allele in combination with an increased function allele. Patients carrying the *1 allele in combination with a no function allele may have decreased concentrations of methadone as compared to patients carrying two no function alleles. 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.