Patients with two copies of the CYP2A6*24A allele or one copy of the *24A allele in combination with one copy of the *1A allele may have decreased metabolism of nicotine as compared to patients with two copies of the *1A allele while patients with one copy of the *24A allele in combination with one copy of the *1A allele may also have decreased metabolism of nicotine as compared to patients with one copy of the *1A allele in combination with the *9 or *12 alleles. However, conflicting evidence has been reported. This annotation only covers the pharmacokinetic relationship between CYP2A6 and nicotine and does not include evidence about clinical outcomes. Other genetic and clinical factors may also affect nicotine metabolism.