by Anthony Roberts - Letrozole (Femara) is a type II (non-steroidal) third generation aromatase inhibitor. Clinically it is used to treat postmenopausal women with either estrogen receptor positive or estrogen receptor unknown breast cancer.

In women, tumors that contain estrogen receptors are classified as estrogen receptor-positive (ER+) tumors. For Letrozole to be prescribed, a given tumor must have been diagnosed as estrogen receptor positive or estrogen receptor unknown.

In the world of bodybuilding it is used to reduce or eliminate excess estrogen caused by the use of aromatizing steroids.

Letrozole was originally sold under the brand name Femara, and produced by the pharmaceutical house Novartis. It was patented on July 25^th, 1997.

Letrozole is known as a type II aromatase inhibitor, meaning, in simplest terms that it attaches to the aromatase enzyme and prevents it from converting androgens to estrogen. In slightly more complex terms, estrogens are produced by the conversion of androgens through the activity of the aromatase enzyme, and letrozole actually inhibits the production of estrogens in by competitive, (reversible) binding to the heme of the relevant cytochrome P450 unit.

Letrozole is currently the most powerful aromatase inhibitor available. In women with breast cancer, it has been shown to reduce estrogen levels by 98% or more (1). However, it’s use and benefits are not limited to eliminating estrogen in women.

In one male test subject Letrozole was able to reduce estrogen levels to undetectable levels (2), and in another clinical study done on both young and elderly men, intravenous administration of Letrozole lowered Estrogen by 46% in the young men tested, and 62% in the elderly subjects. Because estrogen is part of the negative feedback loop of the HPTA, Letrozole (and other anti-estrogens) are able to raise testosterone in male subjects. Letrozole was studied in men, and found to significantly increase LH levels to a 339 and 323% in the young and the elderly, respectively and Testosterone by 146 and 99%, respectively. (3) Letrozole was also able to produce a peak LH response to Gonadatropin Releasing Hormone equal to a 152 and 52% increase from baseline in either young or older men, respectively (3). In a similar study 0.02 mg of Letrozole increased testosterone by 45% after 2 days. (4) That same twenty micrograms of Letrozole was also enough, in one study done on men, to reduce estrogen levels by roughly a third. (4)

Letrozole has a 2-4 day half-life, and it needs to be taken for up to 60 days to get a steady blood plasma level (5).

Letrozole was used in a rodent study to effectively destroy (benign) breast tissue tumors (6), which may potentially indicate its use in males attempting to remove gynecomastia (aka gyno).

As estrogen is also a factor in stopping linear bone growth, Letrozole is currently being examined for potential use in delay of growth seen in children.

In the world of bodybuilding where more is often thought to be better, Letrozole stands almost alone as an exception to that rule. Estrogen is necessary for healthy immune function, healthy cholesterol levels, joint health, cognitive function, and even aids in muscle growth. In my own experience as well as the experience of many bodybuilders and athletes I’ve worked with, Letrozole simply causes estrogen to be reduced to levels too low to function properly. Personally, I suffered a near career-ending knee injury while using 2.5mgs a day of this stuff, and had one of the worst (and longest) bout with the flu I’ve ever had. In my own particular case, I had been using it to eliminate gyno (which it did). I started at a dose of 2.5mgs/day and reduced it by .25mgs every week until the gyno showed no signs of coming back. Unfortunately, this compromised my immune system and joint integrity.

For most recreational steroid users, Letrozole is going to be too harsh, and cause too many problems. Still, people can use it effectively if they don’t use the manufacturer’s clinical dose (2.5mgs) and instead keep their dose to .25-1mg. There are, however, better choices for an anti-estrogen. I should mention that using Letrozole at such a low dose does happen to make it a very good economic choice compared with other aromatase inhibitors.

For pre-contest bodybuilders, Letrozole is almost a necessity to eliminate water retention and achieve the ripped look necessary to compete in today’s bodybuilding world. However, in my experience, it is only necessary to be used for the last 4-6 weeks, to eliminate excess estrogen and water retention. After using Letrozole I recommend staying away from any estrogen suppression for at least a month to try to normalize the body.

Letrozole is the chemical name of active ingredient in Femara. Femara is a registered trademark of Novartis Pharmaceuticals Corporation in the United States and/or other countries.

Letrozole Resources

Femara Prescribing Information

1. Clin Cancer Res. 2005 Apr 15;11(8):2809-21.
2. Epilepsy Behav. 2004 Apr;5(2):260-3
3. J Clin Endocrinol Metab. 2005 Oct;90(10):5717-22. Epub 2005 Jul Comparative assessment in young and elderly men of the gonadotropin response to aromatase inhibition. T'Sjoen GG, Giagulli VA, Delva H, Crabbe P, De Bacquer D, Kaufman JM.
4. Open dose-finding study of a new potent and selective nonsteroidal aromatase inhibitor, CGS 20 267[Letrozole], in healthy male subjects PF Trunet, P Mueller, AS Bhatnagar, I Dickes, G Monnet and G White. Research and Development Department, CIBA-GEIGY Limited, Basel, Switzerland.
5. Clin Cancer Res. 2003 Jan;9(1 Pt 2):468S-72S. Department of Endocrinology, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium
6. J Steroid Biochem Mol Biol. 2001 Dec;79(1-5):27-34. Aromatase overexpression transgenic mice model: cell type specific expression and use of letrozole to abrogate mammary hyperplasia without affecting normal physiology

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