Growth and development are major aspects of paediatric populations that are not readily apparent in adults. The process of growth and development encompasses a series of biological processes which greatly influence the pharmacology of medications in children, specifically their pharmacokinetics, which refers to what the body does to a drug, and can be summarised using the acronym ADME: absorption, distribution, metabolism, and elimination. Such influence is linked to alterations in body composition, the maturation of organs and organ systems, and changes in their respective functions, for example, swallowing reflexes, excretion of digestive enzymes, intestinal motility, transit time and intestinal transporters and drug metabolising enzymes. For example, changes in drug efflux transporters result in a decrease or increase in expelling drugs back into the intestinal lumen and thereby in variation in oral bioavailability. Understanding how development can alter drug performance aids in guiding paediatric therapy.