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Is Hormone Replacement Therapy Safe? Bioidentical vs Synthetic Hormones.

Bioidentical. The word just sounds cleaner and safer than the word “synthetic”. Both of these descriptor words are used to describe hormones. But what are they really? Where do they come from? Is there really a difference?

Medicine is more than a profession. These days, it is an industry riddled with gimmicky sales pitches. It is hard to know what is what with all the information out there! Read below to learn more about hormones that can be given to replace what our bodies no longer make or that are not doing a good job of making.

Conventional medicine has come up with “synthetic” versions of our body’s hormones. They are not exact copies of what our bodies make. They have a different molecular structure. They are made in a lab from animal parts or urine. They act like our natural hormones in certain ways. Some have extra functions that our natural hormones do not have, and some lack functions our natural hormones do. Two examples of this are conjugated equine estrogen (brand name is Premarin) or Medroxyprogesterone (brand name is Provera).

“Bioidentical” hormones are also made in a lab from soy or yams, so technically they are synthetic as well. They get the label “bioidentical” because the end-product is an EXACT copy of what our bodies make. The molecular structure cannot be differentiated from what our bodies make if we were to look at them under a microscope. Since they are an exact replica, they have the same exact function as what our natural hormones have—nothing extra, nothing less. Examples of some bioidentical estrogen hormones are Estrace, Climara, Vivelle, Minivelle, and Estring. Bioidentical progesterone is prescribed as progesterone or micronized progesterone. All of these can be found at any commercial pharmacy, or can be compounded at a specialty pharmacy.

These differences between bioidentical and synthetic hormones are important because it confers different side effect and safety profiles. Many of the studies refer to when counseling patients on risks of hormone replacement therapy are studies that only include synthetic hormones. Unfortunately, these studies cannot (and should not) be applied to bioidentical hormones, since they are different compounds all together.

When the decision to start a patient on hormone replacement is being discussed, a patient must have a thorough medical history and family history reviewed by a provider who is well trained in hormone therapy. The risks of hormone therapy differ depending on type, dose, duration of use, route of administration, timing of initiation, and whether a progestogen is used. Treatment must be individualized using the best available evidence to maximize benefits and minimize risks based on each patient’s specific medical background. For example, if you have a history of a deep vein blood clotting disorder, personal history of breast cancer, a first degree relative (mom or sister) with breast cancer, ovarian or uterine cancer, or high blood pressure, you may not be a candidate for hormone therapy of any kind. If you are post-menopausal, it is also important for your provider to know how long it has been since you have gone through the menopausal transition.

Once you and your provider decide on a hormone treatment plan, it is very important to review this plan periodically to review the benefits and risks of continuing therapy. While the age of 65 years is often seen as the end-point for hormone therapy, ACOG and the North American Menopause Society do not necessarily recommend cessation of hormone replacement at that age.

The most important thing to remember when seeking out hormone replacement or optimization is to see a provider who is well versed in all types of hormone replacement and who is comfortable discussing the literature with you. Medicine is an ever-changing field of study and our knowledge is expanding rapidly. Your provider must be abreast of changes the field they specialize in so they can provide you with the best guidance that is tailored to your personal needs.


1. The 2012 hormone therapy position statement of: The North American Menopause Society. Menopause 2012;19:257-271.

2. The 2022 hormone therapy position statement of The North American Menopause Society. Menopause: The Journal of The North American Menopause Society Vol. 29, No. 7, pp. 767-794.

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