Bioidentical hormone replacement therapy
"Bioidentical" hormone replacement therapy (BHRT) is the use of supplemental doses of steroid hormones with a chemical structure identical to endogenous human hormones (hormones naturally produced in the human body).  Generally BHRT is prescribed to relieve the symptoms of menopause, though more recent therapies promise anti-aging effects and possible deferral of the diseases of aging.  BHRT differs from conventional hormone replacement therapy, which by definition uses animal or synthetic hormones whose structures differ from those produced in the human body.

# 'Bioidentical'
The term "bioidentical" denotes hormones that are chemically synthesized so as to be identical to the endogenous (natural) hormones of the human body: estradiol, estrone, estriol, progesterone, and testosterone.  Because bioidentical hormones are natural, they are not patentable.  Small studies have indicated that these supplemental bioidentical synthetic hormones are safer than, and as effective as, non-identical (patentable) synthetic or animal hormones, and the FDA has permitted the marketing of approved bioidentical hormones in standardized formulations.  However large trials to conclusively establish the apparent advantages of bioidentical hormones have yet to be conducted.  Since the funding for costly large-scale studies is normally advanced in prospect of anticipated large profits from the resulting patent, it is doubtful such trials will ever be conducted unless through governmental financing.
Non-bioidentical synthetic progesterone analogues (called progestins) are often confused with the natural hormone progesterone, but progestins are a suspected human carcinogen.  Estrogens in general have been declared to be known carcinogens.  Such overbroad declarations overlook the potential of bioidentical estriol to actually reduce breast cancer risk.
Bioidentical hormone replacement therapy has received increasing attention since the results of the WHI studies were announced.  The Women's Health Initiative was a large hormone replacement therapy clinical trial which, surprisingly for its corporate sponsors, showed dangerous cancer and clot-inducing properties of Premarin and synthetic progestins.  When these results were publicized and became better known, the use of Premarin and Progestins plummeted (and rates of cancer soon followed).  At the same time, patients and prescribing physicians began to pursue the alternative of prescribing bioidentical hormones with renewed interest.  The apparent advantages of bioidentical hormones have been promoted by, among others, Suzanne Somers.

# Potential advantages over conventional hormone replacement therapy
- Emphasis on topical administration; avoids problems such as blood clotting that are caused by the rapid metabolism of orally administered hormones 
- Progesterone may work differently in the body than medroxyprogesterone acetate
- Individualized compounded doses may be prescribed, rather than "one dose fits all" approach of conventional hormone replacement therapy
- Inclusion of estriol may be protective against hormone-induced cancer. Unlike estradiol, estriol binds preferentially to the second estrogen receptor (ERbeta). ERbeta may function as a tumor suppressor.
Patentable drugs are extensively tested. In the absence of similar testing, the potential benefits of BHRT remain unconfirmed. BHRT may present risks for breast cancer similar to those posed by conventional HRT, or the inclusion of estriol may obviate these risks.  A pilot study conducted by the U.S. National Institutes of Health indicated that the risks of blood clotting and strokes that arise with Premarin and PremPro are sharply lower or nonexistent with bioidentical esterified estrogens.  Oral conjugatged equine estrogens (Premarin) were found to be associated with increased venous thrombotic risk.  In sharp contrast, the study found that users of esterified estrogen had no increase in venous thrombotic risk.

# The Basics of bioidentical hormone replacement therapy
Bioidentical hormone replacement therapy is used to help treat the symptoms of menopause, perimenopause, and post-menopause. Treatment with bioidentical hormones usually includes creating a unique cocktail of hormones for the individual patient, based on hormone deficiencies identified via saliva samples.  These are often referred to as "custom-compounded" hormone products.  The major benefit of this type of treatment is that doses are individualized, and the mixture of products may not be commercially available.  However, although the estrogen and/or progestogen components are government approved, the mixtures themselves are not, as they have not been studied to confirm that they are absorbed appropriately or provide predictable levels in blood and tissue.
Bioidentical hormones, sometimes referred to as natural hormones, are those that are molecularly identical to the hormones that are produced in the body.  Hormones and steroids are taken from plants and animals and altered to be identical in molecular structure, then put into a form that can be absorbed by the body: cream, oral, suppository or injections.  The plants that the hormones are extracted from are soy and yams, while the animals are pigs or horses.  Although these hormones become molecularly identical to the ones humans produce, they cannot be considered completely natural due to the fact that they are altered in a laboratory.
Below is a partial list of bioidentical and non-bioidentical products:

## Bioidentical estrogen
- Micronized estradiol/Estrace - synthesized (soy and yam)
- Estradiol/Alora - synthetic
- Estradiol/Climara - synthesized (soy)
- Estradiol/Estraderm -  synthesized (yam)
- Estradiol/Fem Patch - synthetic
- Estradiol/Vivelle Dot - synthesized (yam)
- Estradiol/Estring - synthesized (yam)
Bioidenticals in standardized formulations have been FDA approved, meeting their standards for purity, potency, efficacy and safety.    Estradiol derived from soy or yam sources is found in FDA-approved medications such as Estrace, the Climara patch and the Vivelle Dot patch.  The lowest-dose approved estrogen is available in Elestrin, a bioidentical estrogen gel approved by the Food and Drug Administration (FDA) in December 2006.  Natural progesterone is marketed under the brand name Prometrium.

## Non-bioidentical estrogen
- Conjugated estrogens/Premarin-Pregnant mares' urine.
- Conjugated estrogens/Cenestin-Synthesized from soy and yams.
- Esterified estrogens (estrone, equilin)/Estra Tab-both estrone and equillin are synthesized from soy and yams.
- Esterified estrogens (estrone, equillin)/Menest-Both estrone and equillin are synthesized from soy and yams.
- Micronized estradiol/Estrace-Synthesized from soy and yams.
- Estropipate/Ogen-Synthesized from Mexican yams.
- Estropipate/Ortho-Est-Synthesized from yams.
- Ethinyl estradiol/Estinyl-Synthesized from Mexican yams.
- Estradiol cypionate/Depo-Estradiol-Synthetic.
- Estradiol valerate/Delestrogen-Synthetic.
Individually-compounded mixtures have not been approved by the FDA, and by their very nature are not susceptible to FDA approval. Consequently, they are untested for purity, potency, efficacy or safety, and some may contain unknown contaminants. Bioidentical estrogen and progesterone are available in FDA-approved forms - estradiol derived from soy or yam sources is found in approved medications such as Estrace, the Climara patch and the Vivelle Dot patch; natural progesterone is marketed under the brand name Prometrium.

# Wiley Protocol
The Wiley Protocol is a controversial type of compounded BHRT that is endorsed by T. S. Wiley and Suzanne Somers. Others have sharply criticized it.