Medication of elderly patients always means special challenges for the caregivers. Aging is characterized by a progressive loss of functional capacities of all organs, reduction of renal GFR, alterations in hepatic clearance of metabolites. The aging process also means altered tissue structures of organs, less cells, usually less receptors and decrease in responses to stimulation and impaired homeostatic mechanisms. The older body is characterized by loss of water content, reduction of muscle mass and increase of fat content in the body. The altered pharmacokinetics and pharmacodynamics in elderly patients can be interpreted with all these changes. An important consideration in treating older adults is that beyond the more common age dependent loss of functional capacities, the older people show a wide variety of physical, psychological, social, and functional characteristics. This heterogeneity also defines a wide scale of pharmacokinetic and pharmacodynamic alterations in the aging organism. Average dose adjustment factors for age neglect the large variation in the declining organ functions among the elderly, which causes great differences in the sensitivity to drugs, irrespective of changes in drug disposition. Thus prescribing medication for older people is challenging because of paucity of clinical trial evidence of therapeutic benefit in this population and the presence of evidence that older people are at increased risk of adverse drug reactions. Beyond these facts, the multimorbidity and frailty of many elderly patients mean extra challenges on the base of drug adverse effects and interactions (polypharmacy). Frailty results from decreased physiologic reserves and multisystem dysregulation with limited capacity to maintain homeostasis and respond to various forms of stress. Frailty is marked by loss of function and increased susceptibility to morbidity and mortality. Knowledge of age-related changes in pharmacology can guide prescribing and help reduce the risk-benefit ratio of using medications in older people.