Physicians will treat larger numbers of elderly patients as the US population ages. Being treated simultaneously for more than 1 condition with multiple prescription drugs is only 1 reason why elderly patients are at greater risk of experiencing adverse drug reactions. The need for physicians to minimize the incidence of these reactions has become incumbent on both physicians and administrators. We review the underlying reasons why the elderly population is at risk of adverse drug reactions and summarize the principles of drug-drug interaction, metabolism, and distribution, which can help elderly patients receive proper pharmacological treatment.