Patients carrying two copies of the CYP3A4*1 allele may have decreased metabolism of tacrolimus as compared to patients carrying two copies of the *1B, *36 or *18B alleles or one copy of the *1 allele in combination with one copy of the *36 or *18 alleles. Patients carrying two copies of the CYP3A4*1 allele may have increased metabolism of tacrolimus as compared to patients carrying two copies of the *22 allele or one copy of the *1 allele in combination with one copy of the *20 or *22 alleles. However, conflicting evidence has been reported. This annotation only covers the pharmacokinetic relationship between CYP3A4 and tacrolimus and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence tacrolimus metabolism.