Pharmacokinetics (PK) studies how the body interacts with supplied chemicals throughout its lifetime (medications for the sake of this article). This is similar to but separate from pharmacodynamics, which investigates the drug’s effect on the body in greater detail. This field typically examines four basic parameters: absorption, distribution, metabolism, and excretion (ADME). Understanding these processes gives practitioners the ability to prescribe and administer medications that will provide the most benefit with the slightest danger and make adjustments as needed, given patients’ diverse physiology and lifestyles. An individual’s physiology influences other elements. Some individual factors can be adequately predicted (e.g., renal failure, obesity, hepatic failure, dehydration), but others are idiosyncratic and have unpredictable effects. Because of individual differences, drug administration must be individualized for each patient, traditionally by empirically changing dosage until the therapeutic goal is accomplished. This method is frequently insufficient since it can delay optimal response or have negative consequences. Understanding pharmacokinetic principles allow prescribers to change dosage more precisely and quickly. Therapeutic drug monitoring is the use of pharmacokinetic principles to personalize medication.