Bioidentical hormones are made in a laboratory. They are based on compounds found in plants (usually soybeans or wild yams).
After the plant-based hormone is processed, its structure is said to be identical to the estrogen, progesterone, or androgen hormone your body makes. (Well-designed studies have yet to prove this theory.) A compounding pharmacist can offer you a custom-made formulation in one of many forms. You might get a capsule, a skin cream or gel, a tablet to dissolve under your tongue, a suppository, or a nose spray. Some commonly prescribed estrogens and progesterones are bioidenticals, such as Estrace (estradiol). There's a major difference between custom-made formulations and commercial products. Commercial products are regulated and tested for purity and potency, but compounding pharmacies are not.
Just like synthetic hormone therapy, bioidentical hormones are prescribed to increase or stabilize a woman's hormone levels. This is most often done during perimenopause, when hormone levels change unpredictably. It's also done after menopause, when the hormones drop to low levels.
The most important fact to remember about taking bioidentical hormones is that the risks are not yet well understood. They may have the same breast cancer, stroke, blood clot, heart disease, and dementia risks that synthetic hormone therapy has.