To achieve high therapeutic efficacy in the patient, information on pharmacokinetics, pharmacodynamics, and pharmacogenetics is required. With the development of science and technology, especially genetic sequencing technology, more and more research on pharmacogenomics has been conducted. The relationship between the genome and the response of a person to drugs is being explored to support personalized medicine, which shows efficacy in clinical treatment. In particular, the IL28B gene polymorphisms have been studied and shown to have impacts on drug responses in the treatment of many diseases, such as chronic hepatitis C, chronic hepatitis B, and myeloproliferative neoplasms. However, pharmacogenetic studies of the IL28B gene have not given exact recommendations for dose adjustment in treatment; they only show the impact tendency that individuals with an unfavorable genotype (usually the genotype of the mutant allele) show poor response to treatment compared to those with a favorable genotype. The frequency of mutant alleles varies among different ethnic groups and between different viral genotypes. Identifying and predicting the possibility of successful treatment helps both clinicians and patients make better choices of treatment decisions to optimize treatment possibilities, and reduce side effects and treatment costs.