Menopause and Hormone Therapy

Does estrogen cause blood clots?

Estrogen is used to treat postmenopausal symptoms such as hot flashes and vaginal dryness. Although it does not cause blood clots, estrogen does increase a woman’s chance of developing a blood clot by two- to fourfold. Most postmenopausal hormone therapies contain both an estrogen and a progestin (synthetic progesterone). Estrogen and progesterone have many effects on a woman’s body, including increasing the levels of clotting factors. For the average woman taking postmenopausal hormone therapy, the absolute risk of a blood clot is small: Only one in 300 women per year who are taking postmenopausal hormone therapy will develop a blood clot. This risk is much higher for a woman who has had a previous blood clot or a woman with thrombophilia.