Testosterone and Aromatase Inhibitors
If you frequent the board on the
Peak Testosterone Forum, you will find that there are
a big percentage of men that are on an aromatase inhibitor, especially Arimidex
(anastrozole). In fact, you'll find that, even though I am attempting to
run a natural men's health web site, I myself am on Arimidex (albeit at a very
low dosage). What gives? Is this sheer hypocrisy or madness?
Or is there a non-disturbing, rational explanation for this?
Before we go into this, let's discuss just what an aromatase inhibitor does.
Aromatase is the enzyme that converts testosterone into estradiol is us men.
As it turns out, both aging and the weight gain that accompanies aging leads to
greater conversion of our testosterone into estradiol, the "bad estrogen", that
is responsible for so many well-known issues in men, including (often) prostate
issues, gynocomastia and erectile/libido/hormonal problems. Aromatase is
in fat cells and as our fat cells expand from a sedentary lifestyle and/or
overeating, we men can easily end up with too much aromatase.
NOTE: Aromatase is also involved in the creation of estrone via conversion from
This is where the aromatase inhibitors come in. They work by binding to
aromatase, thus taking it "out of commission". So why would so many men be
on AI's (aromatase inhibitors)? First of all, a
few men on the
have tried aromatase inhibitors for medical reasons.
Here are a couple of examples:
1. Gynocomastia. As mentioned above, estradiol can play a
major role in gynocomastia. Two of the aromatase inhibitors (letrozole and
anastrozole) are used quite commonly to prevent gyno. (Tomoxifen, which is
not an AI, is also used.)
2. Fertility. Arimidex is often used when men want to raise
testosterone and yet preserve their fertility. I couple of studies have
shown that it will slash estradiol, of course, and simultaneously raise
testosterone, giving a nice boost in a man's testosterone-to-estradiol ratio.
These usages of AI's are relatively uncommon. however, and it is Arimidex's
usage in HRT (testosterone therapy) that is has now become increasingly common.
From what I have seen, if a man goes over a total testosterone of about 600
ng/dl, he will very likely need an aromatase inhibitor. In fact, one of
the biggest reasons that I see for issues with HRT is when doctors do not treat
the elevated estradiol levels that can occur boosting a man's testosterone.
The symptoms are very similar to those for low testosterone: mood crashes,
loss of libido, erectile dysfunction and so on.
That said, many doctors do know about the importance of managing estradiol with
testosterone replacement and will give their patients Arimidex. The dosage
is usually very low - .5 to 1.0 mg/ week split it into two - compared to that
given to prostate or breat cancer patients. Many men are now going to HRT
clinics as well and these almost universally prescribe Arimidex, because
testosterone levels are typically pushed into the 800-1200 range (peak).
The purpose of the Arimidex is to get men into the 20-30 pg/ml range. And
there have been literally dozens of men on Arimidex on the forum following this
or a similar protocol.
It should be pointed out though that men can easily get over high estradiol
levels from the following situations as well:
1. Being overweight.
2. Being on Clomid to boost testosterone (and preserve testicular function
and fertility) or get off of HRT.
3. Being on HCG Monotherapy. (See my page on HCG Monotherapy
So, if you put all these cases together, many more men may be using an aromatase
inhibitor than you might think, especially as testosterone therapies, both
standard and alternative, have grown and expanded in popularity over the last
decade. And almost all of them are using Arimidex.
Why, then, the Arimidex obsession? Well, first of all, it is now quite
reasonably priced after going generic a couple of years ago. And it has
broad application and relatively few side effects if a) used at a lower dosage
and b) plasma estradiol levels are regularly monitored and managed.
NOTE: Arimidex is very powerful and higher dosages (1 mg/day) will lower
"estradiol by approximately 70% within 24 hours and by approximately 80% after
14 days of daily dosing."  Other studies have shown that you can get
even greater reduction in estradiol levels however. 
However, there are definitely other aromatase inhibitor options out there and a
couple of them may be more applicable, i.e. discuss with your doctor if
1. Letrozole (Femara).
One study (in women) showed that Arimidex could achieve almost total suppression
of estradiol levels but was still detectable. However, letrozole was even
more powerful and could achieve total suppression of estradiol to where it could
not even be detected!  Now you have to be careful in going too low with
estradiol as it can actually be dangerous and lead to osteoporosis, mood and
erectile issues, etc., something I document in my link on "Do Men Need Estrogen?".
However, in some cases, that slight extra horsepower from letrozole can help
with gynocomastia, at least according to the "common knowledge" on the steroid
forums. The general feedback is that anastrozole can prevent gyno usually, but
letrozole can actually reverse it (in some cases). Discuss with your
physician of course.
2. Suicide Inhibitors (such as Aromasin). These "type I" type of
aromaste inhibitors do their work using a little different technique: they
actually bind to the aromatase enzyme and permanently and irreversibly take it
out of commission. This may seem really ugly, but the body rebuilds those
enzymes after a few weeks usually. These type of inhibitors are popular in
the steroid community and men that are doing HRT on their own (which I don't
advise). However, I have not seen many HRT clinics, urologists, endos or
PCPs. using them.
One study on young men showed that 25 and 50 mg dosages both reduced plasma
estradiol levels by about a third in 14 days, which is not a bad reduction. 
I cover these types of aromatase inhibitors in more detail in my link on
SIDE EFFECTS: Side effects are minimal on these drugs assuming that estradiol levels are
kept in a safe range. Most of the nasty side effects come from men and women who
have greatly suppressed their estradiol due to cancer treatment. However, it should be
pointed out that Arimidex, for example, affects liver enzymes and may also raise
inflammatory cytokines. I hope to do a page on this soon.
2) Journal of Clinical Oncology, Feb 1 2002, 20(3):751-757, "Influence of
Letrozole and Anastrozole on Total Body Aromatization and Plasma Estrogen Levels
in Postmenopausal Breast Cancer Patients Evaluated in a Randomized, Cross-Over
3) The Journal of Clinical Endocrinology & Metabolism, Dec 1 2003
88(12):5951-5956, "Pharmacokinetics and Dose Finding of a Potent Aromatase
Inhibitor, Aromasin (Exemestane), in Young Males"