Bioidentical hormone therapy: Treatment with hormone medications that contain hormones that have the same chemical formula as those made naturally in the body, referred to by many as "bioidentical" hormones. Bioidentical hormones are created in a laboratory by altering compounds derived from naturally-occurring plant products and are typically taken in the form of creams or gels. There has been increasing interest in recent years in the use of this type of hormone therapy for perimenopausal women instead of conventional hormone therapy with synthetic hormones. Some bioidentical hormone preparations are U.S. FDA-approved and manufactured by drug companies, while others are made at special pharmacies called compounding pharmacies, which make the preparations on a case-by-case basis for each patient. These individual preparations are not regulated by the FDA, because compounded products are not standardized.
Advocates of bioidentical hormone therapy argue that the products, applied as creams or gels, are absorbed into the body in their active form without the need for "first pass" metabolism in the liver and that their use may avoid potentially dangerous side effects of synthetic hormones used in conventional hormone therapy. However, studies to establish the long-term safety and effectiveness of these products have not been carried out.