Blood clot risk varies with estrogen pills

"If our results are confirmed, women seeking menopausal treatment and their providers would find this information helpful when selecting a drug," says Nicholas L. Smith. (Credit: milo tobin/Flickr)

Of two types of estrogen taken as pills to treat menopause symptoms, one is associated with a lower risk of blood vessel clots.

A recent observational study compares the safety of estradiol and conjugated equine estrogen. Of the two, estradiol was associated with a lower risk of leg vein and lung clots.

Researchers find that women patients at Group Health Cooperative who were prescribed estradiol had fewer of these blood vessel clots than did those prescribed Premarin. Estradiol is a generic, bio-equivalent estrogen. Premarin, a patented drug, is a conjugated equine estrogen.


University of Washington and Group Health Research Institute conducted the study. The results will be published this week in JAMA Internal Medicine.

“Although oral estrogens are effective for managing menopause symptoms, not enough is known about the cardiovascular safety of different oral hormone therapy products relative to each other,” says first author Nicholas L. Smith, professor of epidemiology at the University of Washington School of Public Health.

To further understand the differences in risk, researchers measured clotting factors in the blood of women who did not develop a clot. Compared with estradiol users, conjugated equine estrogen users had levels that made them more prone to form blood clots, the researchers find.

The researchers also investigated the risk of heart attack and stroke, and find:

  • The risk of heart attack was somewhat, but not significantly, higher in women using oral conjugated equine estrogens than in those using oral estradiol.
  • No difference in the risk of stroke.

“If our results are confirmed,” Smith adds, “women seeking menopausal treatment and their providers would find this information helpful when selecting a drug.”

This project, part of the Heart and Vascular Health study, included 384 Group Health members, aged 30 to 79, who were taking oral estrogen for menopause symptoms from 2003 through 2009. Menopausal symptoms can include hot flashes, night sweats and vaginal dryness, burning, and irritation.

On February 1, 2005, Group Health’s pharmacy formulary (list of medicines) switched its preferred oral estrogen from conjugated equine estrogens to estradiol. The Heart and Vascular Health study is a case-control study in which Group Health members who have experienced cardiovascular events, such as heart attack or stroke, are matched with members who have not.

Co-authors contributed from the University Hospitals of Geneva, Switzerland; Leiden University Medical Center; and University of Washington.

The National Heart, Lung, and Blood Institute of the National Institutes of Health supported the Heart and Vascular Health study.

Source: University of Washington