The Role of Pharmacogenetics in Predicting Drug Response and Adverse Drug Reactions

Give the same dose of the same drug to two patients, and one may be cured while the other is harmed—a problem as old as prescribing itself. Much of that variability is written in the genome. Pharmacogenetics, the study of how inherited variation modifies drug response, has matured from a laboratory curiosity into a clinical discipline with published dosing guidelines for more than a hundred drugs. This narrative review traces the field from its accidental discoveries—haemolysis in G6PD-deficient soldiers given primaquine, prolonged paralysis after suxamethonium, decades of genotype-blind warfarin dosing—to the modern era of international implementation consortia, pre emptive panel testing, and point-of-care clinical decision support.