Traditional one-size-fits-all drug prescribing leads to therapeutic failures and adverse drug reactions in 15-30% of patients. Pharmacogenomics offers precision medicine approaches by analyzing how genetic variations affect drug metabolism and efficacy. This study investigated genetic polymorphisms in CYP2D6, CYP2C19, and TPMT enzymes among 1,247 participants from diverse ethnic backgrounds, correlating genotypes with drug response phenotypes for common medications including warfarin, clopidogrel, and codeine. Results reveal significant inter-ethnic variations in allele frequencies and drug response patterns. We developed a clinical decision support algorithm achieving 91% accuracy in predicting optimal drug dosing. The research provides frameworks for implementing pharmacogenomic testing in resource-limited healthcare settings.