According to news reports, two of the main reasons doctors are hesitant to prescribe bioidentical hormones are the lack of long-term studies about their safety and inconsistencies with how some of these hormones are made.
The FDA sent The Oprah Show this official statement: "The FDA does not recognize the terms 'BHRT' and 'bioidentical.' Many compounding pharmacies use 'bioidentical' as a marketing term to imply that drugs are natural or have effects identical to those from hormones made by the body. FDA is not aware of credible scientific evidence to support these claims. There are potentially serious adverse effects associated with long term use of these products—even when consumers use FDA-approved hormone therapy drugs that have been proven safe and effective. FDA recommends that women use these products at as low a dosage and for the shortest amount of time necessary."