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 a similar response to tropisetron as compared to patients with two decreased or no function alleles or a no function allele in combination with a normal or decreased function allele, while patients carrying the *1 allele in combination with alleles that result in a normal metabolizer phenotype may have a deceased response to tropisetron as compared to patients with two increased function alleles or an increased function allele in combination with a normal function allele or a deceased function allele with an activity value of 0.5 or patients with an increased function allele with an activity value of 3 or greater in combination with a no function allele or a decreased function allele with an activity value of 0.25. Be aware that the CPIC guideline for tropisetron and CYP2D6 has a 'no recommendation' for CYP2D6 intermediate and poor metabolizers. Other genetic and clinical factors may also influence response to tropisetron.