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Femara: Full Drug Profile

Medically reviewed by Min Clinic Staff | Updated: January 2026

Femara - General Information

Femara (INN, trade name Femara®) is an oral non-steroidal aromatase inhibitor that has been introduced for the adjuvant treatment of hormonally-responsive breast cancer
Estrogens are produced by the conversion of androgens through the activity of the aromatase enzyme. Femara blocks production of estrogens in this way 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. In contrast, the antiestrogenic action of tamoxifen, the major medical therapy prior to the arrival of aromatase inhibitors, is due to its interfering with the estrogen receptor, rather than inhibiting estrogen production.
Femara 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 Femara are often accompanied by prescriptions of osteoporosis-fighting medication such as Fosamax.
Femara has shown to reduce estrogen levels by 98 percent while raising testosterone levels. 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. Usage above 2.5 mg/day is known to potentially temporarily kill sex drive. Above 5mg/day for extended periods may cause kidney problems.
Femara has also been shown to delay the fusing of the growth plates in adolescents. This may boost the effectiveness of growth hormone, and thus Femara is used to treat adolescents and children with short stature.

 

Pharmacology of Femara

Femara is an aromatase inhibitor used in the treatment of breast cancer. Aromatase inhibitors work by inhibiting the action of the enzyme aromatase, which converts androgens into estrogens by a process called aromatization. As breast tissue is stimulated by estrogens, decreasing their production is a way of suppressing recurrence of the breast tumor tissue.

 

Femara for patients

 

Femara Interactions

Clinical interaction studies with cimetidine and warfarin indicated that the coadministration of Femara with these drugs does not result in clinically- significant drug interactions. (See CLINICAL PHARMACOLOGY)

Coadministration of Femara and tamoxifen 20 mg daily resulted in a reduction of letrozole plasma levels by 38% on average. There is no clinical experience to date on the use of Femara in combination with other anticancer agents.

Drug/Laboratory Test-Interactions

None observed.

 

Femara Contraindications

Femara (letrozole tablets) is contraindicated in patients with known hypersensitivity to Femara or any of its excipients.

 

Additional information about Femara

Femara Indication

For the extended adjuvant treatment of early breast cancer in postmenopausal women who have received 5 years of adjuvant tamoxifen therapy. Also for first-line treatment of postmenopausal women with hormone receptor positive or hormone receptor unknown locally advanced or metastatic breast cancer. Also indicated for the treatment of advanced breast cancer in postmenopausal women with disease progression following antiestrogen therapy.

Mechanism Of Action
Femara is a nonsteroidal competitive inhibitor of the aromatase enzyme system; it inhibits the conversion of androgens to estrogens. In adult nontumor- and tumorbearing female animals, letrozole is as effective as ovariectomy in reducing uterine weight, elevating serum Leuteinizing hormone (LH), and causing the regression of estrogen-dependent tumors. In contrast to ovariectomy, treatment with letrozole does not lead to an increase in serum (folicile stimulating hormone (FSH). Femara selectively inhibits gonadal steroidogenesis but has no significant effect on adrenal mineralocorticoid or glucocorticoid synthesis.
Food Interactions
Take without regard to meals. Food slows absorption without decreasing the quantity absorbed.
Generic Name
Letrozole
Synonyms
Letrozol
Drug Category
Antineoplastic Agents; Aromatase Inhibitors
Drug Type
Small Molecule; Approved
Other Brand Names containing Letrozole
Femara;
Absorption
Rapidly and completely absorbed. Absorption is not affected by food.
Biotransformation
Primarily hepatic via CYP3A4 and CYP2A6. Letrozole inhibits the aromatase enzyme by competitively binding to the heme of the cytochrome P450 subunit of the enzyme, resulting in a reduction of estrogen biosynthesis in all tissues. It is metabolized slowly to an inactive metabolite whose glucuronide conjugate is excreted renally, representing the major clearance pathway.
Half Life
2 days
Dosage Forms of Femara
Tablet Oral
Chemical IUPAC Name
4-[(4-cyanophenyl)-(1,2,4-triazol-1-yl)methyl]benzonitrile
Chemical Formula
C17H11N5
Organisms Affected
Humans and other mammals