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Bioidentical HRT was developed by various physicians in the early 1980’s.  Most practioners drew on their knowledge of biochemistry and the estrogen excretion of fertile females, and developed unique treatment strategies for their patients.  Uniform BHRT dosing does not exist per say.  There are various experts in the field that have different philosophies on dosing and the cycling of the hormones which other practitioners use as guidelines.  Most physicians use compounds of Biest or Triest.  Biest contains 20% E₂ and 80% E₃. Triest contains 10% E₁, 10% E₂ and 80% E₃.  

The Tale of Three Estrogens:

Estrone (E₁) http://www.icgeb.org/~p450srv/ligand/estrone.gif

Estrone is widely used alone in commercial preparations such as Orth-Est and Ogen.  However, it is thought to be procarcinogenic in the breast and endometrium at high doses.  It is the largest component of Premarin (75-80% E₁)²

Estradiol (E₂) http://www.icgeb.org/~p450srv/ligand/estradiol.gif

Estradiol is the main estrogen secreted by the ovaries.  Estradiol is also widely used in commercial preparations such as Premarin.  It has been shown to protect against osteoporosis and cardiovascular disease and increase HDL.  High doses appear to stimulate carcinoma of the breast and endometrium and it should be opposed by estriol².

Estriol (E₃) http://histoirechimie.free.fr/Estriol.gif

Estriol is converted from estrone primarily in the liver.  It is rapidly metabolized and binds fleetingly to estrogen receptors.  It and progesterone are the hormones made in the greatest quantities during pregnancy.  It has always been considered a weak estrogen.  There is some evidence that estriol is antineoplastic or at least has less of a potential to cause cancer than E₁ or E₂³. 

Estriol does have advantages over other estrogens³

• Better than estradiol to treat urinary tract infections

• Most beneficial to the vagina, cervix, and vulva for vaginal dryness treatment

• Benefits of other estrogens witout the risks

• Estriol leaves the body more quickly than estradiol and estrone

• Estriol is breast-tissue protective, not proliferative

2. Drisko, JA. Natural isomolecular hormone replacement: an evidence based medicine approach.  International Journal of Pharmaceutical Compounding vol.4 no.6, 2000.

3. Taylor, M. Unconventional Estrogens: Estriol, Biest, and Triest. Clinical Obstetrics and gynecology vol.44 no.4 pp864-879, 2001