The prevalence of obesity has soared in recent decades, and now is considered as a worldwide problem, with significant health and medical implications. Obesity is often linked to several co-morbidities including diabetes, cardiovascular diseases, and cancers, and a number of drugs are available for the treatment of these diseases. Moreover, obesity can affect various physiological factors including plasma proteins, drug metabolizing enzymes, drug transporters, and blood flow, thereby altering drug absorption, distribution, metabolism, and excretion (ADME). Therefore, information regarding obesity-related physiological changes and their pharmacokinetic consequences is crucial for understanding pharmacokinetics and optimizing drug therapy in obese population. Herein, this article reviews the effects of obesity on physiological factors determining drug ADME and their pharmacokinetic consequences. In addition, a brief summary on animal models of obesity is presented.