The CYP2D6*10 allele is assigned as a decreased function allele with an activity value of 0.25 by CPIC. Patients carrying the *10 allele in combination with a no function allele or another decreased function allele with an activity value of 0.25 may have lower clearance of flecainide as compared to patients carrying alleles that result in a normal metabolizer phenotype. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence flecainide metabolism. This annotation only covers the pharmacokinetic relationship between CYP2D6 and flecainide and does not include evidence about clinical outcomes.