The SLCO1B1*15 allele (defined as consisting of both rs4149056 and rs2306283) is assigned as a no function allele by CPIC. Patients carrying SLCO1B1*5 allele in combination with a normal, no, or increased function allele may have a higher risk of lovastatin-related myopathy when treated with lovastatin as compared to patients with two normal function alleles. Other genetic and clinical factors may also influence the toxicity of simvastatin.