Oral contraceptives contain a synthetic progestin, for example norethindrone, which prevents ovulation yet allows women to maintain an otherwise normal menstrual cycle.

Synthetic progestin is a man-made hormone that mimics the effects of progesterone, a natural hormone produced by the ovaries. Norethindrone is an example of a synthetic progestin used in oral contraceptives. When taken, it suppresses the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. Both LH and FSH are essential for the normal menstrual cycle and ovulation. By suppressing these hormones, synthetic progestin prevents the maturation of ovarian follicles and stops ovulation from occurring.

Despite inhibiting ovulation, oral contraceptives containing synthetic progestin still allow for a normal menstrual cycle. This is achieved by maintaining stable hormone levels throughout the cycle. The synthetic progestin maintains the endometrial lining and causes some hormonal fluctuations that mimic the natural cycle. When the oral contraceptive is stopped, typically for a week, the drop in synthetic progestin and other hormone levels cause the uterine lining to shed, leading to a withdrawal bleeding similar to menstruation. In summary, oral contraceptives containing synthetic progestin, like norethindrone, prevent ovulation by suppressing the secretion of LH and FSH, while allowing women to maintain a normal menstrual cycle by mimicking the hormonal fluctuations required for a stable endometrial lining and withdrawal bleeding.