Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Exemestane makes you slimmer and more muscular


Exemestane, the active ingredient in Pfizer's Aromasin [structural formula shown below], truly is a body recompositioning drug. At least it is if you're prepared to accept the results of an Italian study in which 33 women used exemestane for a period of 2 years.

Exemestane is an aromatase inhibitor with a steroid skeleton. Apart from the ethyl group on C6, the compound bears a striking resemblance to boldenone. If the enzyme aromatase which converts androstenedione and testosterone into estradiol tries to provide exemestane with an aromatic ring, it gets so stuck that it breaks down. This is how exemestane lowers oestrogen levels.

Once women with an estradiol-sensitive form of cancer have undergone chemotherapy, an operation and radiation therapy, they usually take anti-oestrogens for five years after that. Most take tamoxifen for a couple of years and then go over to an anti-oestrogen like anastrozole or exemestane. Little is known about the long-term effects of exemestane, hence the Italian research.


The researchers monitored 68 older women for 2 years. All the women had already been taking 20 mg tamoxifen daily for 2-3 years. Half of them continued with this and the other half started taking 25 mg exemestane per day instead.

The exemestane group built up lean body mass. In the two years that the trial lasted the women in that group gained an average of 2.2 kg lean body mass. And the same group lost an average of 0.7 kg fat. The figures below show the effects as a percentage.

Exemestane makes you slimmer and more muscular

Exemestane makes you slimmer and more muscular

Exemestane makes you slimmer and more muscular

The triglyceride levels in the blood of the women in the exemestane group went down a positive development. At the same time exemestane increased the levels of LDL [bad cholesterol] and reduced the concentration of HDL [good cholesterol] a negative development.

Androgenic and anabolic
American cancer researchers have offered an explanation of how exemestane might cause these effects. Exemestane itself has almost no androgenic effect, but the researchers announced in 2007 that an exemestane metabolite the 17beta-hydroxy analogue - is capable of interacting with the androgen receptor. [Mol Cancer Ther. 2007 Nov;6(11):2817-27.]

This means that women should consider carefully whether to use exemestane or not. It also means that exemestane is now of interest to chemical athletes with modest aims.

If men take 25 mg exemestane daily their testosterone level rises by a third, researchers at Farmitalia discovered in the 1980s. [J Steroid Biochem. 1988; 30(1-6): 391-4.] A dose of 50 mg does the same.

So what would happen if you got men to take 25 mg or 50 mg exemestane daily for a year? And if those men were to do weight training as well?

Eur J Intern Med. 2008 Dec;19(8):592-7.