Obesity is now the leading health problem of the 21st century. Weight reduction by conservative methods including diet and exercise has had poor success rates. There has been a substantial increase in the use of bariatric surgery to provide sustained weight loss and thus a reduction in the medical comorbidities that are associated with obesity. However, because these procedures may alter the anatomical and physiological aspects of the gastrointestinal system, there is a possibility of altered pharmacokinetics to medications particularly when taken orally. Furthermore, patients typically lose anywhere from 50 to 75% of their estimated excess body mass approximately one to two years following surgery. This successful therapeutic outcome of the surgery may be causing long term changes in the pharmacokinetics that are independent of any direct anatomical or physiologic changes induced by the procedure.