--- - |2 Summary Over the past 2 decades, knowledge of the role and clinical value of pharmacogenetic markers has expanded so that individualized pre‐emptive therapy based on genetic background of patients could be within reach for clinical implementation. This is evidenced from the frequent updating of drug labels that incorporates pharmacogenetic information (where compelling data become available) by the regulatory agencies (such as the US FDA), and the periodical publication of guidelines of specific therapeutic recommendations based on the results of pharmacogenetic tests by the pharmacogenetics working groups or consortiums of professional bodies. Clinical relevance of the cytochrome P450 (CYP) polymorphism related to dose, effectiveness and/or toxicity of key drugs are presented in this review, including that of warfarin, clopidogrel, tricyclic antidepressants, and proton pump inhibitors. Prospect for routine clinical application of CYP genotyping before prescribing drugs is still currently unclear due to challenges and barriers associated with availability of well‐defined and validated pharmacogenetic studies, the interpretation, result reporting and potential error of genotype testing, involvement of non‐genetic factors, and other patient's demographic and disease conditions. Further studies to provide additional supporting clinical data and acceleration of pharmacogenetic testing standards and techniques should help improve the evidence base needed for clinical utility and hence move the implementation of genotype‐guided therapy in clinical practice a step closer to reality. - Clinical and Experimental Pharmacology and Physiology, Volume 45, Issue 10, Page 991-1001, October 2018.