Oral contraceptive pills (OCPs) are the most popular form of reversible contraception in the United States. Most commonly used OCPs contain a combination of estrogen and progestin. However the efficacy of OCPs is due primarily to the suppression of ovulation that results from the dose of progestin. Changes in the absorption volume of distribution metabolism or excretion of a medication may change its pharmacologic potency. For some medications the volume of distribution for a given dose in an obese individual is greater than the volume of distribution for a thinner individual. In addition in obese patients drugs that undergo Phase II metabolism (or a conjugation reaction with glucuronic acid sulfonates glutathione or amino acids) tend to be metabolized more rapidly thus shortening their duration of action. Increasing body weight has been shown to change rates of estradiol metabolism in young women. Time to reach steady-state levels of levonorgestrel after ingestion appears to be twice as long among obese women compared with women of normal weight; therefore the interval until hypothalamic-pituitary-ovarian activity is suppressed may be lengthened placing obese women at higher risk for ovulation. Our goal was to summarize and evaluate the existing literature addressing the question of whether women with increased weight or body mass index (BMI) have an increased risk of OCP failure compared with normal weight women. This is an issue of public health importance both because obesity is reaching epidemic proportions in the United States and because pregnancy complications are more likely to occur among obese women than thinner women. (excerpt)