The CYP2D6*1 allele is assigned as a normal function allele by CPIC. Patients carrying the *1 allele in combination with alleles that result in a normal metabolizer phenotype may have decreased metabolism of haloperidol as compared to patients carrying two increased function alleles or an increased function allele in combination with a normal function allele. Patients carrying the *1 allele in combination with alleles that result in a normal metabolizer phenotype may also have decreased metabolism of haloperidol as compared to patients carrying an increased function allele with an activity value of 3 or greater in combination with a decreased or no function allele but increased metabolism of haloperidol as compared to patients with a no function allele in combination with a decreased or normal function allele or two decreased or no function alleles. Be aware that the DPWG guideline for haloperidol and CYP2D6 has a 'no recommendation' for intermediate metabolizers. This annotation only covers the pharmacokinetic relationship between CYP2D6 and haloperidol and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence haloperidol metabolism.