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Letrozole [such as Femara by Novartis Pharma] belongs to the substance group of aromatase, through the conversion of androgens into estrogens on the peripheral cells in the body part are blocked. So among other things the estrogen levels will be reduced by taking letrozole (according to studies up to 75%). This is interesting especially for bodybuilders, who use AAS (Anabolic/Androgenic Steroids) to counteract the side effects. Still, letrozole in bodybuilding cycles is used to support the fat reduction and to promote a dry and tough appearance of muscle during the preparation of the competition.

Aromatase inhibitors like letrozole blocks the aromatase enzyme. This procedure reduces the conversion of testosterone into estrogen. Letrozole is an aromatase inhibitor competing with testosterone. These are also called type II aromatase inhibitors.

Estrogen blocker like tamoxifen (Nolvadex) or clomiphene (clomid) can reduce estrogen-related side effects of Anabolic Androgenic Steroids (AAS) sufficient in most cases. These aromatase inhibitors are on one hand cheaper than letrozole and on the other hand they affect positively the cholesterol levels, as they have an effect similar to that of cholesterol in the liver. Letrozole is used today mainly in bodybuilding competition preparation, because as already described, it supports fat loss as well as the draining of the muscles and lowers estrogen levels. Normal training bodybuilders take in mass phase approvingly in purchase, which they put on during the construction phase of water, but are exposed and there are fewer side effects.

In bodybuilding cycles, there is an ongoing existing rumor that Gynecomastia can be eliminated completely by the mere use of letrozole. This is however to consider with caution. In the case of Gyno, you should always consult a doctor.

After a steroid treatment, letrozole is likely taken to return the body’s hormone production. The lifting effect of the testosterone levels and of the LH hormone levels letrozole helps to stimulate the body’s own testosterone production again.

The field of application of the active substance letrozole in medicine:

Most forms of breast cancer can be encouraged in their growth by the female sex hormone estrogen. Letrozole is used against hormone-dependent breast cancers in women after the menopause, to devalue the growth rate of the tumor. It is employed as anti-cancer drug in patients undergoing artificial menopause by the removal of the ovaries.

The mode of action of letrozole:

Estrogen promotes the growth of the cancer and the seeding of cancer cells in the rest of the body (metastases) in estrogen-sensitive tumors. With the withdrawal of estrogen, this special tumors such as breast cancer growth comes to a standstill. Some drugs take advantage of this fact. These include also the active substances from the Group of aromatase inhibitors such as the letrozole. Like all aromatase, the active ingredient of blocking aromatase enzyme is important for the formation of estrogen.

Before menopause, the ovaries are the headquarters of the estrogen by aromatase. The ovaries are aromatase inhibitors but ineffective and can not suppress estrogen production. In addition, a small amount of estrogen in the liver, adrenal glands, is formed by aromatase in the fat tissue cells and – fatally – also in breast cancer cells. In these tissues, the estrogen production continues to run after the menopause. Now, however, it may be blocked by the ingestion of letrozole. Therefore also the production of estrogen, which is remaining after the menopause is brought to the succumb.

In the medical field, the dosage of the aromatase inhibitor letrozole at 2, 5 mg per day. Has been shown in various clinical studies but that, already with doses of 0.1 to 0.5 mg 75% suppression of estrogen production can be obtained.

Bodybuilder letrozole is used frequently during doping to counteract the estrogen side effects. Dosages are usually far below those in the medical field, so doses for the reduction of estrogen-related side effects are, 0, 25 mg up to 1, 25 mg letrozole to meet every two days. Because of the active substance letrozole has a half-life of more than two days (approximately 50 hours) taking enough every other day usually.

Side effects (common):

Sweats, joint pain, hot flashes, fatigue, weakness, loss of appetite, increased appetite, excess cholesterol in the blood, depression, headaches, dizziness, nausea and vomiting, heartburn, constipation, diarrhea, hair loss, rash, muscle pain, bone pain, loss of bone mass (osteoporosis), bone fractures, malaise, water retention in the arms and legs, weight gain.

Side effects (occasional):

Urinary tract infections, lack of white blood cells, water retention in the tissue, anxiety disorders including nervousness, irritability, drowsiness, sleep disorders, memory disorders, sensory disturbances, numbness, taste disorders, cataracts, eye irritation, blurred vision, palpitations, rapid heart beat, acute thrombosis, rise in blood pressure, shortness of breath, abdominal pain, mucosal inflammation, dry mouth, liver enzyme increase in value, itching, dry skin, hives, joint inflammation, frequent urination, vaginal bleeding, vaginal discharge, dry vagina, chest pain, fever, dry mucous membranes, thirst, weight loss.

Stroke, closure of the pulmonary arteries, General artery closures, stroke.

Known interactions with other drugs:

Among other things, the enzyme cytochrome-P-450 2A6 is hindered by letrozole. Substances that are decomposed and are toxic even at slight overdose of this enzyme should not be taken.

Letrozole may not apply with women, who are still not in menopause (menopause) or have a corresponding hormone levels in the blood.

The active ingredient only under medical supervision should be used in patients with hepatic or renal impairment.

The doctor before starting treatment with the drug and continue at regular intervals must measure bone density in patients with osteoporosis or patients who had fractures. If necessary, preventive measures should be taken or begun with a treatment of bone mass loss.

Dosage / application:

Letrozole is administered by default in medicine at doses of 2.5 mg / day.

Bodybuilders use letrozole in the development phase, in combination with steroids at a dose of 0.25 – 1, 25 mg every 2-3 days. Doses are to be found up to 2, 5 mg/day during the competition phase. The taking is prohibited during pregnancy or lactation.

The dosage information here are not recommendations by medical advice. It’s information used by bodybuilders who use r have used these drugs. The dosages are never as generally valid. If you have the intention to use steroids or similar products, ask a doctor or pharmacist.

Studies / availability:

Letrozole is approved as a prescription drug since March 2006 in Germany, in Switzerland since 1997. It can be obtained with a relevant prescription in the Pharmacy. The price is between: 180-240 euro for 30 tablets 2, 5mg active ingredient.

On the black market copies with the same active ingredient are available at various underground Labs. Price for 30 tablets of 2.5 mg active ingredient is between 100-150 euro.

Letrozole is moderately available on the black market.


Letrozol, 4,4-(1H-1,2,4-Triazol-1-ylmethylen)dibenzonitril, Letrozolum, Femara letrozole, Femera

Trade name / manufacturer:

Femara / Novartis Pharma GmbH
Letrozole Onkovis 2, 5mg film-coated tablets / onkovis GmbH
Letrozole 2.5 mg film-coated tablets / CT – pharmaceutical products GmbH CT
LetroHEXAL 2.5 mg film-coated tablets / HEXAL AG

Chemical information:Letrozol Letrozole Molekularformel

Molecular formula: C17H11N5
Molecular weight: 285.303 g/mol
Mono-isotopic mass: 285.101440 da
Half life: 50 hours

Letrozole’s is a white yellowish crystalline powder that is practically odourless.

It is soluble in dichloromethane, moderately soluble in ethanol, and insoluble in water.

Letrozole is a very sensitive substance and should be kept constant at 25 degrees Celsius. Do not expose to a temperature of more than 30 degrees Celsius. The storage environment must be dry.

Letrozole (Femara) film-coated tablets contain also the following, not medically effective ingredients: iron oxide hydrate (E 172), colloidal silicon dioxide, hypromellose, Lactosemonohydrat, MACROGOL 8000, magnesium stearate, microcrystalline cellulose, Poly(O-carboxymethyl)stärke-Natriumsalz, corn starch, talc, titanium dioxide (E 171)

4,4′-(1H-1,2,4-TRIAZOL-1-YLMETHYLENE)  BIS-BENZONITRILE; FEMARA; CGS-20267; LETROZOLE; LetrozoleUsp28; Letrozole99%; CGS-20267,  Femara; LETRAZOLE; letrozolex; Lelrozol; 1-[BIS(4-CYANOPHENYL)METHYL]-1,2,4-TRIAZOLE; 4,4′-(1H-1,2,4-Triazol-1-ylmethylene)di benzonitrile; LETROZOL; 4,4′-(1H-1,2,4-Triazole-1-ylmethylene)bisbenzonitrile; 4,4′-[(1H-1,2,4-Triazole-1-yl)methylene]dibenzonitrile

IUPAC Name: 4-[(4-cyanophenyl)-(1,2,4-triazol-1-yl)methyl]benzonitrile

CAS Register Nummer: 112809-51-5