Patients with one or two copies of the HLA-C*04:01:01:01 allele may have an increased risk of experiencing drug hypersensitivity, including cutaneous adverse reactions, when treated with nevirapine as compared to patients with no HLA-C*04:01:01:01 alleles or who are negative for the HLA-C*04:01:01:01 test. However, conflicting evidence has been reported. Other genetic and clinical factors may also affect risk of nevirapine-induced hypersensitivity.