Patients with two copies of the CYP2A6*9A allele or one copy of the *9A allele in combination with one copy of the *1A, *4A, *12, *26 or *35 alleles may have decreased metabolism of nicotine as compared to patients with two copies of the *1A allele, while patients with two copies of the *9A allele may also have decreased metabolism of nicotine as compared to patients with one copy of the *1A allele and one copy of the *9A or *12 alleles. Patients with one copy of the *9A allele in combination with one copy of the *4A allele may also have decreased metabolism of nicotine as compared to patients with one copy of the *1A allele in combination with one copy of the *4A allele. 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.