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

But the Food and Drug Administration says these alternative hormone mixes are no safer, and told seven makers to stop selling them.

The FDA said it sent warning letters to the companies saying their claims about the "bio-identical hormone replacement therapy" or BHRT products are not supported by medical evidence and are considered false and misleading.

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

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

Compounded drugs are not reviewed by the FDA for safety and effectiveness, and FDA encourages patients to use FDA-approved drugs whenever possible, the agency said.

The warning letters say the pharmacy operations violate federal law by making false and misleading claims about their hormone therapy drugs.

Following a 2002 study that found replacement hormones made by drug companies raised the risk of heart attacks, breast cancer and strokes, many women 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 weather the worst symptoms of menopause.

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