Shares of drug giant

Wyeth

(WYE)

were falling sharply Tuesday after a large study of hormone replacement therapy in postmenopausal women was halted early because the drugs caused an increased risk for breast cancer and heart disease.

The Madison, N.J.-based pharmaceutical firm is the maker of the top-selling hormone replacement medicines. The Premarin family of products racked up more than $2 billion in sales for Wyeth in 2001.

Wyeth is down $8.49, or 17.4%, to $40.75 in recent trading.

The federal study of 16,000 postmenopausal women, known as the Women's Health Initiative, was stopped early because small but significant safety risks of hormone replacement therapy were found to outweigh the benefits. Specifically, the study found that for every 10,000 women taking the drug for a year, 8 more would develop breast cancer compared with an equal number of women taking a placebo. The study also found a small increase in the risk of heart disease, stroke and blood clots.

The findings are groundbreaking because about 6 million women take drugs containing estrogen and progestin to replace hormones that are lost naturally after menopause. The therapy is used to relieve the uncomfortable symptoms of menopause, such as hot flashes, but also because it was believed to improve a woman's overall health.

Wyeth markets the drugs Premphase and Prempro to postmenopausal women who need hormone replacement therapy that includes estrogen and progestin. The company also sells Premarin, which contains only estrogen and is prescribed for women whose uteri have been removed. An 11,000-woman study of estrogen-only replacement therapy is still continuing.

Wyeth is informing doctors of the results of the Women's Health Initiative study, but the company is also urging caution.

"These are valuable new data with significant implications. However, it is also important to recognize the critical role that combination HRT plays in treating the symptoms of menopause, the No. 1 reason that women start therapy," said Dr. Victoria Kusiak, Wyeth vice president, clinical affairs, and North American medical director. In a recent survey, doctors report that management of symptoms is a treatment goal for nine out of 10 new patient starts with combination HRT, the company said.