Targeting Drug Metabolism in Psychiatry: Pharmacogenetic Insights into CYP2D6 and CYP2C19

Introduction:: Pharmacogenetics is revolutionising psychiatric care by providing insights into how genetic variants, particularly in CYP2D6 and CYP2C19, affect drug metabolism, efficacy, and side effects. These insights help clinicians tailor treatment for drugs such as SSRIs, tricyclic antidepressants, and antipsychotics, reducing trial-and-error prescribing and improving patient outcomes. This study aims to investigate the influence of genetic variations, particularly in CYP2D6 and CYP2C19, on drug metabolism, therapeutic effectiveness, and adverse effects in psychiatric treatment. Methods:: This systematic review integrates information from PharmGKB and the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines, as well as data from PubMed, Medline, Scopus, Web of Science, Google Scholar, and reputable health organisations using keywords related to the study topic. Inclusion criteria encompassed peerreviewed articles, studies in English, and research published within the last 10 years. Exclusion criteria included non-relevant or duplicate studies. The selection process followed PRISMA guidelines, with data extraction focusing on study design, outcomes, and reliability to ensure transparency and credibility. The review also examines new findings, such as polygenic risk scores and expanded multigene testing platforms, and highlights clinically relevant gene–drug interactions, including the effect of CYP2D6 polymorphisms on risperidone metabolism. Results:: This study emphasises the significant role of pharmacogenetics in psychiatric treatment, specifically regarding genetic variants in CYP2D6 and CYP2C19. These genetic factors influence treatment with SSRIs, tricyclic antidepressants, and antipsychotics by altering medication metabolism, effectiveness, and adverse effects. The study examines key gene–drug interactions and emerging technologies such as polygenic risk scores, utilising data from PharmGKB, CPIC recommendations, and major medical databases. Discussion:: Despite its promise, widespread implementation faces challenges such as cost, accessibility, and the need for clinician education. Addressing these obstacles through improved insurance coverage and integration of electronic health records can advance precision medicine, thereby enhancing patient outcomes and reducing adverse effects. The gap can be narrowed by employing strategies such as increasing insurance coverage for testing and incorporating genetic decision-support tools into electronic health records. Conclusion:: Integrating pharmacogenetics into psychiatric care can improve treatment safety and precision. For broad adoption, challenges such as cost, test accessibility, and physician education must be addressed. This review supports a future in which pharmacogenetic insights guide psychiatric care to improve treatment outcomes and reduce adverse drug reactions.