What is Femara® (letrozole)?

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Femara® (letrozole) is a type of hormone therapy used to treat breast cancer in certain people. It is used as:1

  • Adjuvant (after initial therapy) treatment for postmenopausal women with hormone receptor-positive (HR+) early breast cancer
  • Extended adjuvant treatment for postmenopausal women with early breast cancer after 5 years of previous treatment with adjuvant tamoxifen
  • First-line treatment for postmenopausal women with HR+ 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.

What are the ingredients in Femara?

The active ingredient in Femara is letrozole.1

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How does letrozole work?

Many breast cancers have receptors for hormones, such as estrogen, on their surfaces. These breast cancers are classified as HR+. When estrogen binds to these receptors, it can fuel the growth and spread of the cancer cells.1

In postmenopausal women, estrogens are created when androgens are converted to estrone and estradiol by the enzyme aromatase. Letrozole stops the body from making estrogens by blocking aromatase. This lowers the amount of estrone and estradiol in the body. This can decrease tumor sizes or delay the growth of tumors.1

What are the possible side effects of letrozole?

The most common side effects of letrozole include:1

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

These are not all the possible side effects of letrozole. Talk to your doctor about what to expect or if you experience any changes that concern you during treatment with letrozole.

Things to know about letrozole

Letrozole may decrease bone mineral density, which may lead to osteoporosis. Your doctor may monitor your bone density during treatment with letrozole.1,2

Letrozole may increase cholesterol levels. Your doctor may monitor your cholesterol during treatment with letrozole.1

Letrozole can harm an unborn baby. If you can become pregnant, you should use birth control during treatment and for some time after the last dose of letrozole. You should also not breastfeed during treatment with letrozole and for some time after the last dose. Talk to your doctor about your options for birth control and breastfeeding while taking letrozole.1,2

Letrozole may cause dizziness, drowsiness, and fatigue. Do not drive or operate machinery until you know how letrozole affects you.2

Before beginning treatment for breast cancer, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.

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