In the Han population of Jiangsu Province, China, the poor metabolic phenotype of CYP2D6 has not been found in clinical samples in our hospital. However, intermediate and poor metabolic phenotypes of CYP2C19 have been detected. Even if clinical reaction is observed, it is difficult to attribute them to metabolic enzyme types being single cause. A large number of genes, enzymes, and proteins are involved in the drug’s in vivo processes. The detection of metabolic enzymes requires comprehensive and cautious judgment in combination with other results of drug metabolism. That is to say, in clinical practice, it is necessary to determine to what extent the metabolic enzyme type affects the peak concentration of the drug and the area of the drug time curve. Is drug gene testing required or actionable? Recommendations related to dosage or adverse reactions are required to be clear rather than vague. Based on these, precise personalized treatment can be implemented specifically on individual patients.