Genetic information helps tailor the starting dose, but patient response can change and many factors influence safety and effectiveness, so ongoing monitoring is essential. Pharmacogenomic data can guide how a drug is metabolized and how someone might respond initially, but it doesn’t capture all the variables that affect therapy over time. Non-genetic factors such as age, organ function (liver and kidney), other illnesses, drug interactions, adherence, diet, and disease progression can shift a drug’s effect or risk profile after the start of treatment. In addition, genetic testing has limitations—not all relevant variants are known or tested for, results may be uncertain, and genotype doesn’t always predict the full phenotype. For example, a genotype might suggest a starting dose for a drug like warfarin, but INR monitoring is still needed because factor fluctuations, interactions, and diet can alter anticoagulation, requiring dosing adjustments. Similarly, even with a pharmacogenomic starting point, clinicians monitor for adverse effects and therapeutic response to ensure safety and efficacy as the patient’s situation evolves.