What are Bioidentical Hormones?

Bioidentical hormone preparations are medications that contain hormones that are an exact chemical match to those naturally produced within the human body.  There is much confusion about the meaning of the term ‘bioidentical hormones’, which are not the same as synthetic hormones, i.e., those man-made hormones traditionally used in hormone replacement therapy (HRT).  More specifically, bioidentical hormones are exactly the same as those made by the female body, i.e., estrogens are 17 beta-estradiol, estrone, and estriol.  Made by drug companies, bioidentical hormones are Food and Drug Administration (FDA) approved and sold in standard doses.

Much of the confusion is due to the illegitimate use of specific buzzwords.  For example, since bioidentical hormones are exactly the same as those made by the body they are often referred to as ‘natural hormones’.  The problem with such labeling is that all natural hormones are not necessarily human in origin.  In the case of Premarin, a very popular hormone used in female HRT, its origin is that of pregnant mares’ urine.  Although natural, Premarin is not bioidentical, at least not to human estrogen.  Similarly, Cenestin (a conjugated/mixture of estrogen hormones used to treat the symptoms of menopause) made from plants is also natural, but again not bioidentical to human estrogen.  The identical quality is the key, so much so, that blood testing of total female estradiol levels reflects both endogenous estradiol and exogenous bioidentical estradiol.  Contrarily, regardless of how Premarin is metabolized into various forms of estrogen, it will not register when total estrogen is measured by standard laboratory tests.  This fact has become a point of contention as advocates of bioidentical hormones argue that estrogen levels can be monitored more precisely, which promotes a greater level of individualized treatment, and believe this to be an advantage over Premarin.  Contrarily, of bioidentical hormone skeptics counter that because exact hormone levels can’t be measured as both endogenous and exogenous in origin, the therapy has no actual aim, and that symptoms not hormone levels should be monitored and treated.

Compounded Bioidentical Hormones

Another type bioidentical hormone preparation, known as compounded bioidentical hormones, are made at special compounding pharmacies on a case-by-case basis for each individual patient.  These custom preparations are not approved by the FDA, because such hormones are not standardized.  However, this in no way diminishes the validity or potency of compounded bioidentical hormones, but rather simply means that they have not been approved for general usage.  For example, such hormones can be especially useful for patients who are allergic to additives found in traditional FDA-approved bioidentical hormones.

Additional caution must be exercised when using compounded bioidentical hormones, which are not subjected to the FDA approval process.   Since they are made on a patient-by-patient basis and do not require FDA approval, they don’t bear the same warnings as their traditional counterparts.  This does not mean that compounded bioidentical hormones are not as safe, as a matter of fact, L.D. King, executive director of the International Academy of Compounding Pharmacists, suggests that patients look for accredited compounding pharmacies listed on the web site of the Pharmaceutical Compounding Accreditation Board (PCAB).  He further cites that it is the job of said boards to ensure that accredited pharmacies adhere to a very high level of practice and extensive quality controls.

However, the vast majority of the women who enter the bioidentical hormone market will not require custom compounded products.  The primary exceptions include women with specific ingredient allergies, and those who not able to tolerate the standardized dosages of traditional bioidentical hormones.

How Long Can Bioidentical Hormones be Administered?

In general, hormone therapy (which has been linked to an increased risk of breast cancer) is administered at the lowest effective dose for the shortest necessary amount of time.  As a relatively new branch of hormone therapy, longitudinal research regarding the total duration of bioidentical hormones administration is lacking.  This doesn’t mean that long-term use of such therapy isn’t safe, quite the contrary actually.  The presumption, in the use of the exact same hormones as one’s body produces, is that it would actually be safer than traditional HRT.  Furthermore, there is no true basis for comparison here since bioidentical hormones are chemically different from synthetic hormone therapy drugs, which are often accompanied by diversity of adverse side effects and have been linked to a variety of potential health risks.

Dr. Erika Schwartz, a practicing MD in New York prescribes both FDA-approved bioidentical hormones and non-FDA compounded bioidentical hormones to her patients.  Schwartz began prescribing bioidentical hormones 14 years ago, and even takes them herself after switching from basic HRT years ago.  Giving her patients a choice between standardized bioidentical hormones and compounded versions, she stresses the importance of doctors being trained on the subject of bioidentical hormones by physicians who are already knowledgeable and using them.  Schwartz is also quick to emphasize the importance of a holistic approach to treatment, and that whether compounded or non-bioidentical hormones are only part of the much larger health picture.  She states, “Sometimes people come in and what they really need is to address their diet, their exercise, their lifestyle.  But if you don’t address them in the context of the whole person — with her diet, her exercise, her lifestyle, with her relationships, with her stresses — and [if] you don’t work with everything, you’re not really going to be able to come up with the results that women would like to see.”

Types, Names, and Forms of Hormones

FDA-approved bioidentical estrogens and micronized progesterones are available with a prescription at local drugstores.  Traditional/commercially available bioidentical estradiol can be found in several forms, but is most often prescribed in pill, cream, patch, and vaginally administered preparations.  Micronized progesterone is most often prescribed in capsule and vaginal gel form.  The below chart (from Harvard Women’s Health Watch, August 2006) provides a fairly comprehensive list of FDA-approved hormones for menopausal symptoms, including the:  type either estrogen, progestin, i.e. micronized progesterone, or combined hormones; brand name; form of preparation; and whether or not it is a bioidentical hormone.  It is also important to note the chart’s four asterisks and their unique caveats.

FDA-approved hormones for menopausal symptoms
Type/source Brand name(s) Preparations Bioidentical?
Conjugated equine estrogens (CEE)/
pregnant mares’ urine
Premarin Pill
Vaginal cream
Synthetic conjugated estrogens/plants Cenestin, Enjuvia Pill No
Esterified estrogens/plants Menest Pill No
17 beta-estradiol/plants
Estrace, others Pill Yes**
Alora, Climara, Esclim, Estraderm, Vivelle, others Patch Yes
Estrogel Transdermal gel Yes
Estrasorb Topical cream Yes
Estrace Vaginal cream+ Yes
Estring Vaginal ring+ Yes
Estropipate (modified estrone)/plants Ortho-Est, Ogen, others Pill No
Ogen Vaginal cream+ No
Estradiol acetate Femring Vaginal ring Yes
Estradiol hemihydrate Vagifem Vaginal tablet+ Yes
Ethinyl estradiol Estinyl Pill No
Progestins, micronized progesterone
Medroxyprogesterone acetate (MPA) Amen, Cycrin, Provera Pill No
Micronized* progesterone USP Prometrium Pill Yes
Prochieve 4% Vaginal gel Yes
Norgestrel Ovrette Pill No
Norethindrone Micronor, Nor-QD, others Pill No
Norethindrone acetate Aygestin, others Pill No
Combined hormones
CEE and MPA Premphase, Prempro Pill No
Ethinyl estradiol and norethindrone acetate Femhrt Pill No
17 beta-estradiol and norethindrone acetate Activella Pill No
Combipatch Patch No++
17 beta-estradiol and norgestimate Prefest Pill No++
17 beta-estradiol and levonorgestrel Climara Pro Patch No++
*Particles are made smaller for better absorption.
**Bioidentical estradiol until ingested and converted in the liver to estrone.
+For vaginal symptoms only.
++The estradiol is bioidentical but not the progestin.

Researching Bioidentical Hormones

Although rather extensively used today, there is still a great deal of skepticism regarding the safety and efficacy of bioidentical hormones, with pro and con arguments on both sides of the fence.  Apparently the best way for a person to determine whether or not bioidentical hormones would be right is through the performance of independent research, i.e., reading reliable source material, actively engaging in subject specific data and information gathering, and via the questioning of family practitioners and those who use presently these types of hormones.

The following sources can be effectively used to jumpstart the research process, but there is no substitute for due diligence:  The American College of Obstetricians and Gynecologists (ACOG); The Mayo Clinic; The Journal of the International Menopause Society; and The Medical Letter on Drugs and Therapeutics.


  • What are bioidentical hormones?
  • Harvard Women’s Health Watch, August 2006
  • Harvard Medical School
  • http://www.health.harvard.edu/newsweek/What-are-bioidentical-hormones.htm
  • Misconception and concerns about bioidentical hormones used for custom-compounded hormone therapy.
  • Bhavnani BR, Stanczyk FZ.
  • J Clin Endocrinol Metab. 2012 Mar;97(3):756-9. doi: 10.1210/jc.2011-2492
  • Report: Limited FDA survey of compounded drug products
  • FDA Center for Drug Evaluation and Research
  • FCER Web site, Jan 28, 2003
  • Bioidentical hormone therapy
  • Files JA, Ko MG, Pruthi S.
  • Mayo Clin Proc. 2011 Jul;86(7):673-80, quiz 680. doi: 10.4065/mcp.2010.0714. Epub 2011 Apr 29
  • PMID:  21531972
  • ACOG Committee on Gynecologic Practice Compounded bioidentical hormones Obstetrics and Gynecology 106:1139-1140, 2005
  • Bio-Identicals: Sorting Myths from Facts
  • FDA consumer update
  • Jan 9, 2008
  • Are bioidentical hormones safer and more effective than hormones used in traditional hormone therapy for menopause symptoms?
  • The Mayo Clinic
  • Mary M. Gallenberg, M.D.
  • http://www.mayoclinic.com/health/bioidentical-hormones/AN01133
  • Bioidentical compounded hormones: a pharmacokinetic evaluation in a randomized clinical trial.
  • Sood R, Warndahl RA, Schroeder DR, Singh RJ, Rhodes DJ, Wahner-Roedler D, Bahn RS, Shuster LT
  • Maturitas. 2013 Apr; 74(4):375-82. Epub 2013 Feb 04.
  • Bioidentical progesterone cream for menopause-related vasomotor symptoms: is it effective?
  • Whelan AM, Jurgens TM, Trinacty M.
  • Ann Pharmacother. 2013 Jan;47(1):112-6. doi: 10.1345/aph.1R362. Epub 2012 Dec 18.

Leave a Reply

Your email address will not be published. Required fields are marked *