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Letromina(Letrozole)(Femara)30t/2.5mg(Alpha Pharma)
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Letromina(Letrozole)(Femara)30t/2.5mg(Alpha Pharma)

Item 12510

Systematic (IUPAC) name


Clinical data

Trade names Femara

AHFS/Drugs.com monograph

MedlinePlus a698004

Licence data US FDA:link

Pregnancy cat. D(US)

Legal status Schedule VII (CA) POM (UK) -only (US)

Routes Oral Pharmacokinetic data

 Bioavailability 99.9%

Protein binding 60%, mainly to albumin

Metabolism pharmacologically-inactive carbinol metabolite (4,4΄-methanol-bisbenzonitrile)[1]

Half-life 2 days[1]

Excretion Kidneys[1] Identifiers

 CAS number 112809-51-5 

 ATC code L02BG04

PubChem CID 3902

DrugBank APRD01066

ChemSpider 3765 


 KEGG D00964 

 ChEBI CHEBI:6413 


 Chemical data

Formula C17H11N5 

Mol. mass 285.303 g/mol

SMILES eMolecules & PubChem



Letrozole (INN, trade name Femara) is an oral non-steroidal aromatase inhibitor for the treatment of hormonally-responsive breast cancer after surgery.

Estrogens are produced by the conversion of androgens through the activity of the aromatase enzyme. Estrogens then bind to an estrogen receptor, which causes cells to divide.

Letrozole prevents the aromatase from producing estrogens by competitive, reversible binding to the heme of its cytochrome P450 unit. The action is specific, and letrozole does not reduce production of mineralo- or corticosteroids.


FDA-approved use


Letrozole is approved by the United States Food and Drug Administration (FDA) for the treatment of local or metastatic breast cancer that is hormone receptor positive or has an unknown receptor status in postmenopausal women. Side effects include signs and symptoms of hypoestrogenism. There is concern that long term use may lead to osteoporosis, which is why prescriptions of Letrozole are often accompanied by prescriptions of osteoporosis-fighting medications such as bisphosphonates.

Off-label use

Letrozole has been used for ovarian stimulation by fertility doctors since 2001—having fewer side-effects than clomifene (Clomid) and less chance of multiple gestation. A Canadian study presented at the American Society of Reproductive Medicine 2005 Conference suggests that Letrozole may increase the risk of birth defects[citation needed]. A more detailed ovulation induction follow-up study found that letrozole, compared with a control group of clomiphene, had significantly lower congenital malformations and chromosomal abnormalities at an overall rate of 2.4% (1.2% major malformations) compared with clomiphene 4.8% (3.0% major malformations).[2] Despite this, India banned the usage of Letrozole in 2011, citing potential risks to infants.[3]

The anti-estrogen action of letrozole has been shown to be useful in pretreatment for termination of pregnancy, in combination with misoprostol. It can be used in place of mifepristone, which is expensive and unavailable in many countries.[4]

The anti-estrogen action of Letrozole is preferred by athletes and bodybuilders for use during a steroid cycle to reduce bloating due to excess water retention and prevent the formation of gynecomastia related breast tissue that is a side effect of some anabolic steroids.[5]

Some studies have shown that Letrozole can be used to promote spermatogenesis in male patients suffering from nonobstructive azoospermia.[6]

Letrozole has also been shown to delay the fusing of the growth plates in mice.[7] When used with growth hormone, Letrozole has been shown thereputic for adolescents and children with short stature.[8]

Letrozole has also been used to treat endometriosis.[9]

Comparison with tamoxifen

Tamoxifen is also used to treat hormonally-responsive breast cancer, but it does so by interfering with the estrogen receptor. However, letrozole is effective only in post-menopausal women, in whom estrogen is produced predominantly in peripheral tissues (i.e. in adipose tissue, like that of the breast) and a number of sites in the brain.[10] In pre-menopausal women, the main source of estrogen is from the ovaries not the peripheral tissues, and letrozole is ineffective.

In the BIG 1-98 Study, of post-menopausal women with hormonally-responsive breast cancer, letrozole reduced the recurrence of cancer, but did not change survival rate, compared to tamoxifen.[11][12]


Letrozole is contraindicated in women having a pre-menopausal hormonal status, during pregnancy and lactation.[13]

Adverse effects

The most common side effects are sweating, hot flashes, arthralgia (joint pain), and fatigue.[13]


Letrozole inhibits the liver enzyme CYP2A6, and to a lesser extent CYP2C19, in vitro, but no relevant interactions with drugs like cimetidine and warfarin have been observed.[13]

See also


  1. ^ a b c 003330 Letrozole
  2. ^ Tulandi T, Martin J, Al-Fadhli R, et al. (June 2006). "Congenital malformations among 911 newborns conceived after infertility treatment with letrozole or clomiphene citrate". Fertility and Sterility 85 (6): 1761–5. doi:10.1016/j.fertnstert.2006.03.014. PMID 16650422.
  3. ^ Sinha, Kounteya (18 October 2011). "Finally, expert panel bans fertility drug Letrozole". The Times of India. Retrieved 14 November 2011.
  4. ^ Vivian Chi Yan Lee, Ernest Hung Yu Ng, William Shu Biu Yeung, Pak Chung Ho. Misoprostol With or Without Letrozole Pretreatment for Termination of Pregnancy. Ob Gyn. Vol 117, No.2, Part 1, February 2011 pp. 317-323
  5. ^ Gynecomastia-Gyno.com: Realistic Treatment Options
  6. ^ Geneviève Patry, Keith Jarvi, Ethan D. Grober, Kirk C. Lo (August 2009). "Use of the aromatase inhibitor letrozole to treat male infertility". Fertility and Sterility 92 (2): 829.e1-829.e2.
  7. ^ R Eshet, G Maor, T Ben Ari, M Ben Eliezer, G Gat-Yablonski, M Phillip (2004). "The aromatase inhibitor letrozole increases epiphyseal growth plate height and tibial length in peripubertal male mice". Journal of Endocrinology 182 (1): 165–172. doi:10.1677/joe.0.1820165. PMID 15225141.
  8. ^ Ping Zhou MD, Bina Shah MD, Kris Prasad PhD, Raphael David MD (2005). "Letrozole Significantly Improves Growth Potential in a Pubertal Boy With Growth Hormone Deficiency". Journal of the American Academy of Pediatrics 115 (2): 245–248. doi:10.1542/peds.2004-1536. PMID 15653791.
  9. ^ Endometriosis ESHRE abstract
  10. ^ Simpson ER (2003). "Sources of estrogen and their importance". The Journal of Steroid Biochemistry and Molecular Biology 86 (3–5): 225–30. doi:10.1016/S0960-0760(03)00360-1. PMID 14623515.
  11. ^ Letrozole therapy alone or in sequence with tamoxifen in women with breast cancer, the BIG 1-98 Collaborative Group, N Engl J Med, 361:766, 2009 Aug 20
  12. ^ 32nd Annual San Antonio Breast Cancer Symposium
  13. ^ a b c Haberfeld, H, ed (2009) (in German). Austria-Codex (2009/2010 ed.). Vienna: Österreichischer Apothekerverlag. ISBN 3-85200-196-X.



Letrozole is the chemical name of Novartis selective third generation aromatase inhibitor (AI), a drug that works by blocking the aromatase enzyme responsible for the production of estrogen.

In clinical use, Letrozole is primarily administered to halt the progression of breast cancer in women. It is generally used as part of an aggressive treatment in post-menopausal women, to fight and reverse the spread of breast cancer after other treatments (such as Tamoxifen therapy) has failed. Its probably the most efficient product on the market for this purpose (5). Letrozole is very similar in both structure and action to its AI predecessor Arimidex.

In athletics and bodybuilding, it is used as an ancillary compound within anabolic steroid cycles for its estrogen reducing properties, and has the additional benefit of modestly increasing testosterone levels. Many anabolic steroids aromatize (convert to estrogen via the aromatase enzyme), a process that is responsible for many of the undesirable side effects which accompany anabolic steroid use such as acne, gynecomastia, water-retention, etc.

Letrozole also does quite a few things that would be of interest to both bodybuilders and athletes. Firstly, it has been shown to reduce estrogen levels by 98% or greater (1). In at least one documented incident, Letrozole reduced test subject estrogen to undetectable levels, while increasing LH, FSH and SHBG (4). For the bodybuilder, less estrogen in the body means less chance of estrogen-related side effects. This makes Letrozole an appropriate choice for even the heaviest bulking or cutting cycles, including those which incorporate harsher androgens. Also, if you are a competitive bodybuilder, Letrozole is a must have product for contest preparation as no other ancillary compound supports the coveted dry and tight appearance quite as well.

An effective dose of Letrozole is .25 to .5mg/day. I use .25mgs/day, but be forewarned, if you go over this amount it can kill your sex drive. Also worth noting is Letrozoles substantial estrogen rebound effect that occurs after discontinuation. Maximum inhibition of the aromatase enzyme has been cited at doses as low as 100 mcg. (2)

Its effects on serum lipids including cholesterol, both HDL and LDL are, in the words of one researcher: "inconsistent." However, you could certainly suffer an impaired lipid profile and immune system if estrogen levels remain too low for long periods of time.

As previously mentioned, Letrozole can be used to raise LH and FSH, these are hormones which signal your testes to produce more testosterone. (6) These properties mean that Letrozole can be used for post-cycle therapy (PCT), and I have successfully used it for this purpose. However, for various reasons, Tamoxifen is a better PCT choice.

How good is Letrozole when compared with Aromasin (Exemestane) and Arimidex (Anastrozole), its primary rivals? Letrozole is 10-20x more potent than Anastrozole, and about as potent (but with a slightly different mechanism) as Exemestane. It also long-lasting. Letrozole has a whopping 2-4 day half-life, and youll need to take Letrozole for approximately 60 days (with wild variance of 2-6 weeks) to achieve a steady blood plasma level (8).

Those are impressive numbers, but heres one of the most interesting things about Letrozole:

It may reduce/eliminate/reverse existing gynecomastia!

In a study conducted on mice (and yes, I know its not perfect), gyno-like changes in the mammary gland were totally destroyed! Heres a direct quote from that study:

Our results also indicate aromatase overexpression-induced changes in mammary glands can be abrogated [destroyed] with very low concentrations of the aromatase inhibitor, letrozole.(7)

In addition, both I and a friend successfully used Letrozole to eliminate our gyno while both using 2.5mgs/day, tapering down to .25mgs/day, and then finally off. The gyno never returned for either of us.

Based on its availability and cost (when you consider the fact that .25mgs/day is more than enough protection from estrogen-related sides on most cycles), not to mention its overall utility for a variety of functions (destroying gyno, preventing estrogenic sides, and for PCT), Id say that this stuff is pretty great.


1. Clin Cancer Res. 2005 Apr 15;11(8):2809-21.
2. J Clin Endocrinol Metab. 1995 Sep;80(9):2658-60.
3. Eur J Obstet Gynecol Reprod Biol. 2002 Nov 15;105(2):161-5
4. Epilepsy Behav. 2004 Apr;5(2):260-3
5. Semin Oncol. 2004 Dec;31(6 Suppl 12):3-8.
6. Diabetes Obes Metab. 2005 May;7(3):211-5.
7. 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.
8. (Clin Cancer Res. 2003 Jan;9(1 Pt 2):468S-72S.).







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