Arimidex®, An Aromatase Inhibitor, Is Not Just For Breast Cancer Anymore!

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Aromatase inhibitors decrease estradiol/estrone blood levels and increase total and free testosterone.

What is an AI?  It stands for Aromatase Inhibitor. This group of medications is an enzyme blocker that slows or stops the conversion of Testosterone into Estrone and Estradiol.  The common use, as stated by the FDA, is for Estrogen receptor positive (ER+) breast cancer, to decrease the estrogen in the bloodstream that comes from testosterone.  In estrogen receptor positive tumors, we attempt to decrease the estrogen of any type so the breast cancer cells are literally starved for estrogen, which causes the cancer to shrink and die and prevents estrogen receptor positive (ER+) breast cancers from metastasizing.

AIs have become the most effective medical (vs surgical) treatment for ER+ Breast Cancer, and Arimidex® is the most common of the AIs because it has the fewest side effects and is the most effective.  This blog is about how doctors use aromatase inhibitors, “off-label”, for many other problems and conditions in both men and women.


What do AIs do?

They decrease estradiol and estrone blood levels and increase total and free testosterone.


What Conditions are AIs used for “off label”?

There are many problems caused by too much estrogen in both men and women.  The following lists are some of the conditions that are aggravated by or caused by too much estrogen in women and men.

  • Endometriosis
  • Fibroids in the uterus
  • Excessive uterine bleeding
  • Breast pain
  • Obesity
  • Infertility caused by anovulation and infrequent periods
  • Polycystic ovaries
  • Short stature
  • Insulin resistance


Problems from too much estrogen in men:

  • Gynecomastia—male breasts
  • Short stature
  • Obesity
  • Infertility
  • Low Testosterone
  • Low free testosterone
  • Insulin resistance


How Do AIs Work? 

The natural process that the body uses to break down testosterone from the ovaries and testes, and androgens from the adrenal gland, to get rid of them and excrete androgens from the body is called aromatization.  The way this happens is that testosterone is broken down by an enzyme called aromatase (p19).  Enzymes are chemicals that break down all types of food, proteins, fats and carbohydrates in our body all day long.  I liken an enzyme’s activity to a shredder in the office.  An enzyme breaks up substances that the body has finished using, or substances that occur in excessive amounts to achieve balance within the body.    The aromatase enzyme is specialized to break down testosterone into estrogens, one step in the process of ridding itself of testosterone.  Other enzymes break down estrogen, and ready it for disposal.

In the conditions and diseases that we listed above, too much estrone is made for a variety of reasons, while the aromatase enzyme is converting testosterone into estrone. For example when a person becomes overweight their fat contains a large amount of aromatase which makes estrogen and increases insulin resistance which causes the individual to make more fat and the process continues to cycle.  When a woman gains over 200 lbs. her aromatase enzyme increases by 70% and the estrogen increases.   The effect on other parts of the body depends on gender.  For women the increased amount of estrogen stimulates the uterus to grow a thick lining and bleed a lot, and fibroids to grow.  Breasts enlarge and hurt. Estrogen also inactivates testosterone so libido and sexual response diminish.  In this case, one of the methods of treatment is to give an aromatase inhibitor to stop the production of more and more estrogen from the fat.  AIs and other meds to decrease insulin resistance are very effective in stopping the cycle of weight gain, and increased estrogen followed by more weight gain.


How is infertility treated in men, by using AIs?  How does it work?

AIs work three ways in men to stimulate fertility.  Testosterone is increased by blocking its conversion into estrone, and in this way AIs increase the total T level.

By decreasing the amount of estrone, the free T increases as well.  AIs also stimulate LH production in the pituitary which stimulates the testes to make more total T, and this stimulates the production of sperm.  This one treatment for men can make all the difference between fathering a child and being childless.


How do AIs increase T in men?

In the same way that AIs treat fertility, they also treat low T.  In general if a man’s testes are young enough, usually younger than 50, Arimidex® can treat low T in young men who have normal testes and high estrone.  In this way we can avoid shutting down a man’s system by replacing testosterone. We can use his own T production and make the most of it without suppressing his natural production.

In men who start producing estrogen early, height will generally be limited.  If we suspect that an adolescent will be unusually short we can block their production of estradiol and estrone with an AI or we can give them growth hormone.  GH is expensive and has many side effects, but AIs have very few side effects in young women who have a generous supply of estrogen.  Both will increase their final height.


Why Are AIs Used For Endometriosis?

Endometriosis is a very common disease in women that causes severe pain, pelvic scarring, infertility and is the most common reason for a woman to have a total hysterectomy.  For the past 30 years we have had medications like LUPRON that totally blocks the production of estrogen and put a woman in temporary menopause to shrink the implants or actually “burn it out”.  There are lots of side effects and problems associated with taking this medication, including osteoporosis and severe hot flashes.

Now we treat endometriosis with Aromatase Inhibitors (eg. Arimidex®) that work locally in the endometriosis implants.  Endometriotic implants actually produce estrone in the implant that is then stimulated by the same estrone causing it to grow, bleed and scar. Arimidex® blocks the aromatase enzyme that makes the estrone in the implants.  This shrinks the implants and gives women the opportunity to avoid total hysterectomy.


What other medications/supplements act like an aromatase inhibitor?

  • Glutamine
  • Nicotine/smoking
  • Nitric Oxide
  • Di- indoylmethane (DIM)



Medications are often created for one reason, to treat one type of disease, and then are found to be profoundly effective for a handful of other diseases, sometimes this is a breakthrough like we have had with Aromatase inhibitors, and many of the conditions we did not have an effective solution for, now have a treatment!

This Health cast was written and presented by Dr. Kathy Maupin, M.D., Bio-identical Hormone Replacement Expert and Author, with Brett Newcomb, MA., LPC., Family Counselor, Presenter and Author.

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