This is not the first time hormone therapy's popularity has plummeted. Since the 1940s, when Canadian drug maker Ayerst developed the estrogen-only drug Premarin, hormone therapy has cycled in and out of the medical world's good graces.

The story of Premarin's rise is recounted in detail in a story published by Harvard University's Health Publications division in May 2004. Soon after Premarin's introduction, drug maker Wyeth acquired Ayerst and, in the 1950s, set its high-powered marketing operation to work selling doctors on the drug's merits.

Their efforts got a big boost in 1966 when gynecologist Robert Wilson published Feminine Forever, a book claiming that menopause was not a phase of life but a disease: "To watch a pleasant energetic woman turn into a dull-minded but sharp-tongued caricature of her former self is one of the saddest of human spectacles," he wrote. Wilson went on to describe estrogen as a "cure" for menopause, telling women it would, among other things, help them look and feel younger and sexier. The book became a best seller, sales of Premarin soared, and by the end of the 1960s some 12 percent of all postmenopausal women were taking estrogen. Years later, Wilson's son told The New York Times that Wyeth-Ayerst had bankrolled the book's publication.

The popularity of Premarin took a hit in 1975, after The New England Journal of Medicine published two studies pointing to an increased risk of endometrial cancer among women who relied solely on estrogen to treat menopausal symptoms. The number of hormone therapy prescriptions fell precipitously. By the early 1980s they had dropped from a peak of 30 million prescriptions per year to approximately half that many.

Scientists, however, did not give up on the therapy, and soon medical guidelines began advising doctors to prescribe progestin in combination with estrogen after studies indicated doing so decreased women's chances of developing cancer. Women gradually began returning to hormone replacement therapies and, by 1999, annual prescriptions reached some 90 million.

But even as patients' fears about hormone therapy seemed to recede, so did research raise new concerns. For a number of years the National Institutes of Health had been testing hormone therapies as part of its Women's Health Initiative. NIH researchers hoped to broaden the scope of hormone replacement therapies, exploring ways in which such therapies might head off the development of chronic diseases such as osteoporosis and cardiovascular disease. Instead, clinical trials were suspended when the researchers discovered that one of the most popular estrogen/progestin combinations, a drug called Prempro, appeared to increase study participants' risk of breast cancer, heart attack and stroke.

The Prempro finding was a bombshell, and millions of women began to question whether the benefits of hormone replacement therapies were worth the risks. Even as subsequent studies indicated that lowered doses of traditional therapies could be safe and effective, many women began searching for non-hormonal relief.