复方口服避孕药（combined oral contraceptives，COCs）由外源性雌孕激素配伍而成，主要是通过高于生理水平的雌孕激素负反馈抑制垂体-卵巢轴，降低内源性促性腺激素和性激素的水平，影响卵泡的发育而避孕。但在周期性的COCs的无活性药间期（hormone-free interval， HFI）会有垂体-卵巢轴活性的恢复，其激素水平的变化及卵泡发育的情况与雌激素的剂量、孕激素的剂型、HFI的改变相关。

The combined oral contraceptives (COCs) are combinations of exogenous estrogen and progestin. The primary mode of action for COCs is thought to be suppression of the pituitary-ovarian axis by higher than physiological levels of estrogen and progestin, secondarily leading to suppression of endogenous gonadotropin and gonadal hormone secretion and ovarian function. During the hormone-free interval (HFI), COCs users experience activation of their pituitary–ovarian axis. The level of hormones and follicular development are associated with the doses of estrogen, progestin formulations and the changes of HFI.