Postmenopausal Hormone Replacement and the Risk for Blood Clots FREE

Two hormones, estrogen and progestin, are often prescribed to women after menopause to prevent thinning of bones. When these hormones are used in oral contraceptive pills, blood clots are a known side effect of treatment. The blood clots usually develop in the deep veins of the leg, a condition called deep venous thrombosis. Parts of these clots can break off and travel through the bloodstream to the lungs, a condition called pulmonary embolism. Although they are usually treatable with blood thinners, deep venous thrombosis and pulmonary embolism can be disabling or even deadly. Despite these concerns, little is known about the risk for blood clots in women who take both estrogen and progestin as postmenopausal hormone replacement therapy.

To find out whether women who take postmenopausal hormone replacement therapy are at a greater risk of developing blood clots than women who do not.

The researchers studied 2763 women who were known to have heart disease and were past menopause but were younger than 80 years old, had not had a hysterectomy, and had never had a blood clot. These women were participating in a larger study of hormone replacement therapy to prevent heart attacks.

The researchers assigned women to receive either hormone replacement therapy with estrogen and progestin or a placebo tablet. The placebo tablet looked identical to the hormone tablet, but it contained no active ingredients. They then followed women over time to see who developed deep venous thrombosis or pulmonary embolism.

After 4 years of follow up, 34 of 1380 women taking the hormone pill had experienced a blood clot compared to 13 out of 1383 women taking the placebo pills. This means that about 1 out of every 263 women treated with hormone replacement therapy will experience a blood clot each year because of the hormonal treatment. Women with leg fractures, cancer, or hospitalization for surgery were more likely to develop a blood clot than were women without these conditions. Women taking aspirin and those taking certain cholesterol-lowering medications were less likely to develop clots than were women not taking these medications.

All of the women in this study had heart disease. The study results might not apply to women without heart disease.

Women and their doctors should consider the potential side effect of blood clots when considering the risks and benefits of hormone replacement therapy after menopause.