Prempro

Dr.

JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital, called the research on bioidentical hormones "very, very sparse." "We need to be cautious about not repeating the debacle that occurred with conventional hormone therapy," said Manson, a leader in the 2002 research on standard hormone replacement therapy.

In a newsletter last September, doctors from the Mayo Clinic similarly warned that "hormones aren't safer or better just because they're labeled natural or bioidentical." Proponents argue that bioidentical hormones won't have the dangerous side effects of oral hormones, such as Key to the approach is not just the hormones used but the way they're delivered.

The only way to get a "bioidentical" substance into the system is non-orally, chiefly through the skin via patches, creams, lotions or gels.

That's because medicines taken orally don't enter the bloodstream in the same form that you take them.

They pass first through the liver, where their chemical structure is altered.

Medicines taken transdermally don't pass through the liver first en route to the bloodstream, and thus aren't altered.

For example, when a woman takes oral estradiol, the hormone that declines precipitously at menopause, it is converted in the liver to estrone, a weaker hormone, said Dr.

Al...