I personally prefer formestane. Below is a great comparison of AI's.
A Very Quick Physiology Lesson
The male body uses an enzyme called aromatase to convert a percentage of susceptible androgens into estrogens. Naturally this includes both those the body produces and those introduced from outside the body such as AAS (Anabolic Androgenic Steroids). In most cases the result is predominantly a very powerful estrogen called estradiol.
Aromatase is present in most body tissues and the circulatory system. Unfortunately fat cells produce a scary amount of this man-altering enzyme…which of course explains why fat guys get boobs. (Yikes!)
When we think of aromatase inhibitors we often assume that they are all the same with various levels of results…depending upon dosages. While the latter may be true, the prior statement certainly is not.
Aromatase Inhibitor "Types"?
Let’s do a quick review of the types of aromatase inhibitors that are available. These include type 1, or steroidal inactivators, and type 2, or nonsteroidal inhibitors. The type 1 aromatase inhibitors include exemestane and formestane and are actually androgen analogues (cool stuff if applied right!). The type 2 inhibitors include aminoglutethimide, anastrozole, letrozole, and vorozole.
There are both similarities and differences between the type 1 and 2 aromatase inhibitors. Their similarities include the fact that both inhibit aromatase in a very specific fashion and reduce endogenous or circulating estrogens. On the other hand, the steroidal inhibitors are rather better classified as inactivators, in that they bind to the aromatase molecule in an irreversible fashion (they hold on and do not let go). Because aromatase is rapidly replaced within the body, however, the significance of this property in terms of clinical benefit is unclear in some ways. In addition, the "inactivators" have a structure quite similar to that of androgens and may, in higher doses, have anabolic steroid or androgen-type properties.
Of the type 2 agents, letrozole tends to be more potent than anastrozole and both are more potent than aminoglutethimide in regard to estrogen production. Of the type 1 agents, exemestane is considerably more potent than formestane. But again in each case this may be dose dependant more so than a question of effectiveness of the drug itself. In vivo (tested in live subjects rather than a test tube), the aromatase inhibitors can be graded as shown in the basic table below.
Relative Potency of Type 1 and Type 2 Aromatase Inhibitors
Product Aromatase Inhibition (%) Residual Aromatase (%)
Formestane/
4-Androstenoldione 91.9 8.1
------------------------0---------------------------------------0--------------------------------------0
Aromasin/
Exemestane 97.9 2.1
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Cytadren/
Aminoglutethimide 90.6 9.4
------------------------0---------------------------------------0--------------------------------------0
Arimidex/
Anastrozole 96.7 3.1
------------------------0---------------------------------------0--------------------------------------0
Femara/
Letrozole 98.7 1.3
-----------------------0---------------------------------------0---------------------------------------0
So far it would appear that Letrozole is the leader, huh?
Anti-Estrogens And IGF-1 Production
GH (Growth Hormone) is like a master hormone for tissue growth and fat regulation due to its own intrinsic qualities and its propensity to be converted into or trigger the production and release of Growth Factors. Of these Growth Factors, one of the best known in regard to muscle growth is IGF-1 (Insulin-Like Growth Factor-1).
As most are aware by now, IGF-1 is a powerful anabolic and anti-catabolic hormone. Whether in pre-contest mode or packing on the mass, the amount of circulating and stored IGF-1 an athlete maintains plays a powerful role in the results achieved. Obviously as IGF-1 levels decrease so does the potential for packing on the beef, and the amount of lean tissue lost during calorie-restricted periods increases as well. (Not good)
Estrogen, and more so estradiol, can trigger GH release from the pituitary gland. Aromatase inhibitors decrease the amount of circulating estrogen/estradiol and estrogen receptor antagonist keep estrogen out of the specific pituitary receptors. So in many regards the use of anti-estrogens can effect IGF-1 production and in some cases affect the number of IGF-1 receptors our tissues posses.
Product Effect Percentage
Formestane/
4-Androstenoldione Increases IGF-1 26%
-------------------------0----------------------------------0-----------------------0
Femara/
Letrozol Increases IGF-1 24%
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Arimidex/
Anastrozole Decreases IGF-1 18%
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Nolvadex/
Tamoxifen Decreases IGF-1 23.5%
-------------------------0----------------------------------0-----------------------0
Faslodex/
Fulvestrant Decreases IGF-1 70%
-------------------------0----------------------------------0-----------------------0
Cytadren/
Aminoglutethimide Increases IGF-1 27%
-------------------------0----------------------------------0-----------------------0
Aromasin/
Exemestane Increases IGF-1 28%
-------------------------0----------------------------------0-----------------------0
Hmmm, so now we have some major points in favor of Cytadren, Aromasin and Formestane.
Other things to consider pre-contest or simply as a matter of achieving desired results at any point in the pursuit of freak status include…
When attempting to evaluate "the best" choice for any item, the question of specific-intent should come into play first. If you asked for solely my opinion, then I would choose the product that covered the greatest number of needs for specific-intent or goal(s). Personally I prefer Formestane (under whatever name the product is provided, in the purest most active form).
Why?
Formestane increases IGF-1 secretion and activity.
Formestane decreases the number of progesterone receptors (inhibits the trenbolone and "deca-dick" type side effects and increases fat loss)
Formestane inhibits 91.9% of aromatase enzyme production
Formestane increases HPTA activity similar to HCG and Clomid together
Formestane is anabolic and androgenic (At 500mg weekly the product is similar in effects to 250mg of Primobolan Enanthate)
Formestane is a "suicide inhibitor" of aromatase. Specifically this means that it will irreversibly bind to the aromatase enzyme and permanently deactivate it
Formestane (The sterile injectable form) possesses a 4-day half-life
Formestane decreases SHBG 34% thus increasing androgen activity.
Formestane inhibits DHT (dehydrotestosterone) formation and activity.
Formestane possesses 1% of the binding affinity of DHT to DHT receptors
Formestane has been shown to decrease prostate concerns such as BPH.
Formestane has been shown to continue to increase HPTA function above natural levels even after 22 weeks of continuous administration.
Oh, As To Water Retention…
Naturally the anti-estrogen value of any of the aromatase inhibitors does decrease the affects of the water retention hormone aldosterone. Those that are androgenic in structure seem to do so better. The point is that though some of the other products discussed do posses these qualities, none but formestane has them all. Fewer drugs or products are always a "better choice".
Cool, But Where Can Formestane Be Found?
The medically prescribed product Formestane is administered as a deep intramuscular injection. It is commonly known as Lentaron I.M. Depot. Its active ingredient is 4-androstenoldione acetate in a pure isomer form. The product is normally administered for breast cancer patients at a dosage of 250mg every 2 weeks to 250mg weekly. Since androstenoldione acetate has a half-life of about 4 days when administered I.M. the dosing protocol has been less than perfect for those athletes whom have opted to utilize it.
