Relief Naturally? Growing numbers of women, scared off hormone replacement therapy (HRT), are betting that "bioidentical," or "natural," hormones offer a safer way to relieve menopausal symptoms such as vaginal dryness and hot flashes. But experts say that assumption is untested. Practitioners of alternative medicine are the biggest prescribers.

What Is This Stuff? Plant-based hormones are processed in the lab from soybeans and chemicals, then synthesized to be molecularly identical to the three estrogens that women's bodies make -- estriol, estrone and estradiol. For a woman with a uterus, these estrogens are commonly mixed with progesterone to avoid increasing the risk of endometrial cancer. Compounding pharmacies (those that mix their own medications) sell the prescription blends in tablets, gels and creams. Common combinations include bi-est (estradiol and estriol) and tri-est (estrone, estradiol, estriol).

Do They Work? So it appears. A study published in 2000 in Obstetrics & Gynecology found that 17beta-estradiol, a common ingredient, reduced hot flashes by 91 percent at some doses. A study in the journal Menopause in 2003 found that estradiol gel relieved the frequency and severity of hot flashes. Claims that they help keep women beautiful, energetic and sexy are, alas, unsubstantiated.

The Rub "Our hypothesis is that they are going to be a bit safer [than HRT] to use, but the hypothesis hasn't been tested," said Jeanne Drisko, program director for the program in integrative medicine at the University of Kansas Medical Center. "The prudent thing to do would be to assume that all estrogens have the same risk" -- meaning increased risk of breast cancer, blood clots, heart attack and stroke, said Anthony Scialli, principal scientist with Center for the Evaluation of Risk to Human Reproduction, part of the National Institutes of Health. Adriane Fugh-Berman, associate professor of physiology and biophysics in Georgetown University School of Medicine's complementary medicine program, said studies show that even women who produce higher levels of estrogen themselves have higher risks of breast cancer. To assume that bioidentical hormones are safe, she said, simply isn't warranted.

-- Elizabeth Agnvall