WASHINGTON - Government health officials began cracking down Wednesday on Internet sales of custom-mixed hormones for menopausal women, a market created when doctors deemed prescription estrogen therapy too risky for many patients.

But the Food and Drug Administration says these alternative hormone mixes are no safer, and the agency told seven makers to stop claiming they are. The FDA also said some mixes contain estriol, which is illegal to be sold in the U.S. because the FDA has not approved it for any use.

In letters to the pharmacies, the FDA said the claims about the "bioidentical hormone replacement therapy" (BHRT) products are not supported by medical evidence and that the pharmacy operations are breaking the law by making false and misleading claims about the drugs.

"We want to assure that Americans receive accurate information about the risks and benefits of drug therapies," the FDA's chief medical officer, Dr. Janet Woodcock, said in a statement.

The agency said it is concerned that the claims for safety and effectiveness mislead patients, doctors and other health care professionals.

In addition to citing the menopausal use, some pharmacies claimed the products could prevent or treat serious diseases, including Alzheimer's, stroke and some cancers, the agency said. Officials said there is no credible evidence to support those claims.

Dr. Kathleen Uhl of the agency's office of women's health said the FDA does not know how widely these drugs are used. But the said the FDA has received a growing number of questions about them.

Women need to know that all drugs have both benefits and risks, and that patients should discuss them with their doctor, Uhl said.

The FDA urges women to use the lowest effective dose of hormone replacement drugs that it has approved for menopausal symptoms, and do so for the shortest time possible.

The agency does not review compounded, or custom-mixed, drugs for safety and effectiveness, and encourages patients to use FDA-approved drugs whenever possible.

A 2002 study found replacement hormones made by drug companies raised the risk of heart attacks, breast cancer and strokes. Since then, many women have turned to the estrogen, progesterone and testosterone products sold by compounding pharmacies.

Medical researchers concluded in 2003 that hormone replacement pills should be taken only as a brief treatment to help women cope with the worst symptoms of menopause.

The drug company Wyeth later complained to the FDA about the Internet sales of compounded products.

L.D. King, executive director of the International Academy of Compounding Pharmacists, charged that the FDA's action will deny hundreds of thousands of women access to many commonly compounded bioidentical hormones, "substituting its judgment for that of doctors."

FDA officials stressed that they are not cracking down on all forms of compounding. Traditional pharmacy compounding involves the combining or altering of ingredients by a pharmacist, in response to a doctor's prescription, to produce a drug tailored to an individual patient's special medical needs.

In addition, it said the term bioidentical has no accepted meaning.

Warning letters went to Panorama Compounding Pharmacy of Lake Balboa, Calif.; Saint John's Medical Plaza Pharmacy of Santa Monica, Calif.; Murray Avenue Apothecary of Pittsburgh; Village Compounding Pharmacy of Houston; Pharmacy Compounding Specialties of Dallas; Reed's Compounding Pharmacy of Tucson, Ariz.; and Pacifica Pharmacy of Torrance, Calif.

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