In the largest clinical trial to date, the combination estrogen-progestin (Prempro) increased the risk of certain serious conditions.
According to the study, over one year, 10,000 women taking estrogen plus progestin might experience:
Seven more cases of heart disease than women taking a placebo
Eight more cases of breast cancer than women taking a placebo
Eight more cases of stroke than women taking a placebo
Eighteen more cases of blood clots than women taking a placebo
An increase in abnormal mammograms, particularly false positives
The study found no increased risk of breast cancer or heart disease among women taking estrogen without progestin. Over one year, however, 10,000 women taking estrogen alone might experience:
Twelve more cases of stroke than women taking a placebo
Six more cases of blood clots in the legs than women taking a placebo
An increase in mammography abnormalities
The effect of hormone therapy on mammograms is important, because it suggests that women on hormone therapy may need more frequent mammograms and additional testing.
Who should consider hormone therapy?
Despite the health risks, estrogen is still the gold standard for treating menopausal symptoms. The absolute risk to an individual woman taking hormone therapy is quite low — possibly low enough to be acceptable to you, depending on your symptoms.
The benefits of short-term hormone therapy may outweigh the risks if you:
Experience moderate to severe hot flashes or other menopausal symptoms
Have lost bone mass and either aren't able to tolerate other treatments or aren't benefitting from other treatments
Stopped having periods before age 40 (premature menopause) or lost normal function of your ovaries before age 40 (premature ovarian failure)
Women who experience premature menopause or premature ovarian failure have a different set of health risks compared with women who reach menopause near the average age of about 50, including:
A lower risk of breast cancer
A higher risk of osteoporosis
A higher risk of coronary heart disease (CHD)
In addition, hormone therapy appears to reduce the risk of osteoporosis and CHD when started soon after menopause in young women. For women who reach menopause prematurely, the protective benefits of hormone therapy may outweigh the risks.