Drug absorption is the fundamental pharmacokinetic process describing the movement of a drug from its site of administration into the systemic circulation. As a core research concept within pharmacology, it investigates the mechanisms, kinetics, and modifying factors influencing this transfer, including drug properties, formulation, physiological conditions, biological barriers, and interactions with other substances or the microbiome. Understanding drug absorption is critical for predicting bioavailability, optimizing dosage regimens, and determining the therapeutic efficacy and safety profile of a medicinal agent.