A primer on the hormone-free interval for combined oral contraceptives

The dosing, schedules, and other aspects of combined oral contraceptive (COC) design have evolved in recent years to address a variety of issues including short- and long-term safety, bleeding profiles, and contraceptive efficacy. In particular, several newer formulations have altered the length of the hormone-free interval (HFI), in order to minimize two key undesired effects that occur during this time: hormone-withdrawal-associated symptoms (HWaS) and follicular development.This primer reviews our current understanding of the key biological processes that occur during the HFI and how this understanding has led to changes in the dosing and schedule of newer COC formulations.In brief, HWaS are common, underappreciated, and a likely contributor to COC discontinuation; because of this, shortening the HFI and/or supplementing with estrogen during the progestin-free interval may provide relief from these symptoms and improve adherence. A short HFI (with or without estrogen supplementation) may also help maintain effective follicular suppression and contraceptive efficacy, even when the overall dose of estrogen throughout the cycle is low.Taken together, the available data about HWaS and follicular activity during the HFI support the rationale for recent COC designs that use a low estrogen dose and a short HFI. The availability of a variety of COC regimens gives physicians a range of choices when selecting the most appropriate COC for each woman's particular priorities and needs.