Side Effects of Premarin Linked to Increased Risk of Blood Clots: Study

Pfizer’s hormone replacement therapy (HRT) drug Premarin may increase a woman’s risk of blood clots, according to researchers from the University of Washington.  

According to a study published in the medical journal JAMA Internal Medicine on September 30, side effects of Premarin may more than double the risk of venous thrombosis when compared to taking oral estradiol for treatment of menopause. The research also suggested that there may be a smaller risk that Premarin could increase the risk of heart attack.

Researchers looked at 385 postmenopausal women between the ages of 30 and 79 who used oral hormone therapy. They found 68 cases of venous thrombosis, 67 myocardial infarction, or heart attack incidents, and 48 cases of ischemic stroke and compared them with 201 matched controls. All were using either Premarin (conjugated equine estrogen) or estradiol, which is sold under the brand names Vagifem, Evamist, Estring and others.

The data appears to indicate that using Premarin may double the risk of blood clots, increase the risk of heart attack by 87% and led to stroke rates that were roughly comparable to oral estradiol. The researchers concluded that women taking Premarin had blood that was more likely to clot, but indicated that there should be efforts to duplicate and confirm the findings.

Premarin is one of three HRT drugs, including Prempro and Provera, that have been linked to serious health concerns in recent years, including an increased risk of breast cancer.

About 10,000 breast cancer lawsuits have been filed by hormone replacement therapy users throughout the United States, raising similar allegations over the side effects of Prempro, Provera and Premarin, which are used to artificially boost hormone levels in women undergoing menopause due to surgery or in postmenopausal women.

In 2002, a study by the Women’s Health Initiative first warned of the risk of breast cancer from hormone replacement therapy, sparking the widespread litigation.

A recent study using data from the Nurse’s Health Study, found an 88% increase in the risk of breast cancer for women who underwent HRT over a period of 10-15 years. The risk doubled if the women used HRT for 15 to 20 years.

Several juries nationwide have awarded multi-million dollar compensatory damage awards to plaintiffs diagnosed with breast cancer after HRT use, including a number of cases that included punitive damage awards after juries found that Wyeth intentionally hid the risks associated with the medications. However, the drug makers have also obtained defense verdicts in a number of cases.