The CYP2B6*1 allele is assigned as a normal function allele by CPIC. Patients carrying CYP2B6*1 allele in combination with another normal function allele may have decreased risk of adverse events (eg. liver toxicity or CNS side effects) when treated with efavirenz as compared to patients with a no or decreased function allele in combination with a normal or increased function allele or with two no or decreased function alleles. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence the toxicity of efavirenz.