The hot flashes came without warning. "I would be on the airplane," said Earlene Bennett, 61, a Northwest Airlines flight attendant. "My face would get real flushed. Here I am with a beverage cart, and I'm sweating to death."

Synthetic hormones helped curb her symptoms, but then they returned. She also worried about reports linking the hormones to breast cancer. So she turned to "bioidenticals," hormones derived from plants, which have the same chemical makeup as a woman's natural hormones.

Now she feels healthier, if not completely at ease. "I don't know if it's safer," she said, "but I'm more comfortable with it."

Bennett's uncertain choice illustrates an important new crossroads in women's health care.

As 40 million women enter menopause, they are stepping into growing disputes among doctors and pharmaceutical companies over how to manage its symptoms -- and hearing more debate over whether menopause should be treated as an illness or a life passage.

The marketplace of medicines for menopausal women is exploding into a nearly $4 billion industry, providing women an array of options. But even as they seek something more than one-size-fits-all treatments, they are getting no clear answers on the safest and most effective forms of relief.

Last month Wyeth, the biggest seller of prescription hormones, called on the Food and Drug Administration to investigate pharmacies that sell and market "custom-mixed" or "custom-compounded" bioidenticals.

Wyeth says it does not object to the many FDA-approved bioidenticals, which undergo stringent scrutiny. It is charging, however, that there is no way to guarantee the safety or efficacy of blends, which use varying amounts of three naturally occurring estrogens, as well as progesterone. The pharmaceutical giant is demanding that pharmacies be required to play by the same rules as other drugmakers.

But pharmacists dismiss such concerns as turf protection by drug companies, some of which sell bioidentical hormones. A lawsuit filed by a group of pharmacies that does custom-compounding seeks protection against FDA actions and probably will be heard next year.

"There is no reason to believe that a custom-compounded product is safer," said Pamela Boggs, director of education of the North American Menopause Society. "It may be more dangerous, because it has never been tested. They are experimental drugs." Others say prescriptions typically are created based on a saliva test, whose accuracy many doctors find suspect.

Supporters of custom-compounding say it results in fewer side effects, may have fewer long-term health risks, and can be tailored to the individual.

"You're putting back in your body something biochemically identical to us," said Sandy Greenquist, a certified nurse midwife and menopause clinician who founded the Menopause Center of United Hospital in St. Paul three years ago. "From a logical perspective, that seems safer to me."

Bennett, who went through menopause at 50, is one of many women finding relief through custom-compounding. She uses a cream that's a mix of estriol, estradiol -- two of the three estrogens -- and progesterone. While not all insurers pay for such prescriptions (up to $50 a month), Bennett's does.

Julie Andersen, 50, of New Hope also uses custom hormones. After a hysterectomy in January, "it was like someone flipped a switch." She suddenly had hot flashes, forgetfulness and other symptoms. Many have disappeared in the months since the Jazzercise franchise owner began taking bioidentical hormones. "I feel like it's given a lot of my younger life back," she said.

A huge and growing market

The market for hormone replacement took an $800 million hit after the Women's Health Initiative's 2002 study linked artificial hormones to increased risks of heart disease, stroke, breast cancer and blood clots. But as waves of baby-boom women enter menopause, the market is expected to hit $4.8 billion by 2010, according to a marketing research company Frost & Sullivan.

A woman officially enters menopause when she has not menstruated for 12 consecutive months. In the United States, the average age of menopause is 51. But symptoms such as hot flashes, mood swings, depression, irregular periods and low libido may begin years before, even in a woman's 30s, in a phase called "perimenopause." Perimenopause can last a decade; on the other end, some women experience post-menopausal symptoms into their 80s.

Until the 20th century, when lifespans increased, menopause was part of the final stage of life. But in the mid-20th century, synthetic estrogens and progesterones were developed to help treat discomfort and have been used by most doctors since. The most common are still Premarin and Provera.