CYP2C19 is a cytochrome P450 monooxygenase primarily involved in metabolizing polyunsaturated fatty acids (PUFA) and xenobiotics. Mechanistically, it catalyzes hydroxylation at the omega-1 position and epoxidation of PUFA double bonds 123, utilizing molecular oxygen with electrons from NADPH via cytochrome P450 reductase. The enzyme also metabolizes therapeutic agents including warfarin, voriconazole, benzodiazepines, sumatriptan, and omeprazole 456. CYP2C19 processes plant monoterpenes like limonene and organophosphate pesticides 7. Clinically, CYP2C19 genetic polymorphisms significantly influence drug pharmacokinetics. Loss-of-function variants (rs4986893, rs3814637) reduce warfarin maintenance dose requirements by 10-34% 4, while *2 and *3 alleles increase voriconazole plasma concentrations in pediatric patients 5. The rs4986893 polymorphism associates with myocardial infarction susceptibility 8. Beyond drug metabolism, CYP2C19 expression correlates with basal ganglia and hippocampal volume, particularly in females, suggesting endogenous substrate metabolism involving steroid hormones and endocannabinoids 9. Clock gene regulation of CYP2C19 expression may enable individualized pharmacotherapy 10.