WEDNESDAY, Oct. 2 (HealthDay News) -- An estrogen drug used by women to relieve hot flashes and other menopausal symptoms is tied to an increased risk for certain types of heart troubles, while another estrogen drug appears to be safer, a new study says.

Researchers compared the cardiovascular safety of the two commonly used pills: Premarin, a so-called "conjugated equine estrogen" and a generic version of estradiol.

Premarin is made from the urine of pregnant mares while estradiol is a "natural" or "bioequivalent" estrogen, according to background information in the study, which was funded by the U.S. National Heart, Lung, and Blood Institute.

Although these estrogen pills "are effective for managing menopause symptoms, not enough is known about the cardiovascular safety of different oral hormone therapy products relative to each other," lead author Nicholas Smith, an affiliate investigator at the Group Health Research Institute, said in a Group Health news release.

The researchers tracked outcomes for 384 postmenopausal women, aged 30 to 79, who were using hormone therapy pills. The women included 68 who had experienced blood clots in the legs and in the lungs, 67 who had a heart attack, as well as 48 who had an ischemic stroke, which occurs due to blocked blood flow to the brain. The other 201 women acted as a control group.

Compared to women who took estradiol, those who took Premarin had a higher risk of blood clots. The women taking Premarin also had a somewhat higher risk of heart attack. There was no difference in ischemic stroke risk, according to the study published online this week in the journal JAMA Internal Medicine.

Smith and his colleagues said that further studies are needed to confirm these findings.

"If confirmed, the results would provide valuable information to women and their health care professionals when making safety decisions regarding available (hormone therapy) options for menopausal symptom management," the researchers concluded.

One other expert agreed that this "small" study is not the final word on this issue.

"Clearly, further studies need to be done, as for many women HRT is part of the treatment for quality of life, and knowing the safest treatment option is crucial," said Dr. Suzanne Steinbaum, director for women and heart disease at Lenox Hill Hospital, in New York City.

More information

The American Academy of Family Physicians has more about hormone replacement therapy.