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JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital, called the research on bioidentical hormones ''very, very sparse," and warned that women should not flock to them.''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 September newsletter, doctors from the Mayo Clinic similarly warned that ''hormones aren't safer or better just because they're labeled natural or bioidentical."So why am I even considering replacing oral hormones with something ''bioidentical"?

Because I like the way they're delivered.

The only way to get a ''bioidentical" substance - that is, an exact chemical match to something the body already makes - into the system is non-orally, chiefly through the skin, via patches, creams, lotions, or gels.

Medicines taken orally don't enter the bloodstream in the same form that you take them because they pass first through the liver, where their chemical structure is altered.

Medicines taken transdermally do not pass through the liver en route to the bloodstream, and hence are not altered.When a woma...