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What is Femara®? (letrozole)

Femara is an aromatase inhibitor, a type of hormone therapy, used to treat breast cancer in certain people1:

  • As an adjuvant (after initial therapy) treatment for postmenopausal women with hormone receptor-positive early breast cancer
  • As an extended adjuvant treatment for postmenopausal women with early breast cancer after 5 years of previous treatment with adjuvant tamoxifen
  • As a first-line treatment for postmenopausal women with hormone receptor-positive or unknown hormone status, advanced or metastatic breast cancer. Letrozole may also be used to treat postmenopausal women with advanced breast cancer who experienced disease progression after treatment with antiestrogen therapy

For certain women with advanced or metastatic breast cancer, letrozole may be used alone or in combination with other treatments, like Kisqali® (ribociclib). Letrozole is manufactured by Novartis Pharmaceuticals.

What is the ingredient in Femara?

The active ingredient in Femara is letrozole, an aromatase inhibitor.1

How does letrozole work?

Many breast cancers have receptors for hormones, such as estrogen, on their surfaces. These breast cancers are classified as hormone receptor-positive (HR+). When estrogen binds to these receptors, it can fuel the growth of the cancer cells and lead to them growing and spreading.

In postmenopausal women, estrogens in the body are created when androgens are converted to estrone and estradiol by the enzyme aromatase. Letrozole inhibits the production of estrogens by blocking aromatase and lowers the amount of estrone and estradiol in the body. This can lead to decreased tumor size or delaying the progression of tumor growth in some women.1

What are some of the possible side effects of letrozole?

The most common side effects experienced by patients taking letrozole include1:

  • Hot flashes
  • Joint pain
  • Flushing (redness in the skin)
  • Weakness or lack of energy
  • Swelling (edema)
  • Headache
  • Dizziness
  • High cholesterol
  • Increased sweating
  • Bone or muscle pain

Letrozole may cause decreases in bone mineral density, which may lead to osteoporosis. Women may need additional screening to monitor their bone density.1,2

Letrozole may increase the levels of cholesterol in the blood. Women may need additional screening to check for increases in cholesterol.1

The most serious side effects experienced with letrozole include bone fractures, decreased bone density, osteoporosis, and high cholesterol.2

Things to know about letrozole

Before starting treatment with letrozole, women should tell their doctor if they are pregnant, or planning to become pregnant. Letrozole should not be used in women who are pregnant, as the drug may cause harm to an unborn baby. Women who can become pregnant should use effective contraception while taking letrozole and for at least three weeks after the last dose of letrozole. Patients should discuss effective contraception methods with their doctor. Letrozole is only approved for use in women who are postmenopausal.2

While receiving letrozole, women may receive bone scans and cholesterol tests to monitor their bone health and cholesterol levels.1

Because some women have reported experiencing dizziness, drowsiness, and fatigue while taking letrozole, women should not drive or operate machinery until they know how letrozole affects them.2

Dosing information

Letrozole comes in a 2.5 mg tablet that is taken by mouth. It may be taken with or without food.1

For more information, read the full prescribing information of letrozole.

Women should discuss with their doctor all medications (prescription and over-the-counter), vitamins, and herbal supplements they are taking prior to starting treatment with letrozole. Some medications or supplements may interfere with each other and may cause side effects.

Patients should take their medication as prescribed by their doctor. Patients should talk to their doctor if they have any questions, or if they have questions regarding their letrozole regimen.

Written by: Editorial Team | Last reviewed: October 2019.
  1. Femara prescribing information. Novartis Pharmaceuticals. Available at https://www.pharma.us.novartis.com/sites/www.pharma.us.novartis.com/files/Femara.pdf. Accessed 9/27/18.
  2. Femara product website. Novartis Pharmaceuticals. Available at https://www.femara.com/. Accessed 9/27/18.