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Generic name: letrozoleLET-roe-zol ]
Drug classes: Aromatase inhibitors, Hormones / antineoplastics

Medically reviewed by Philip Thornton, DipPharm. Last updated on May 23, 2023.

What is Femara?

Femara lowers estrogen levels in postmenopausal women, which may slow the growth of certain types of breast tumors that need estrogen to grow in the body.

Femara is used to treat breast cancer in postmenopausal women. It is often given to women who have been taking tamoxifen (Nolvadex, Soltamox) for 5 years.


Femara can harm an unborn baby or cause birth defects. Do not use if you are pregnant.

Before taking Femara, tell your doctor if you have osteoporosis, high cholesterol, or liver disease (especially cirrhosis).

Femara may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert. To be sure this medicine is helping your condition, your blood may need to be tested often. Your bone mineral density may also need to be checked. Visit your doctor regularly.

Tell your doctor about all other medicines you use, especially tamoxifen (Soltamox).

Before taking this medicine

You should not use Femara if you are allergic to letrozole, or if you have:

  • if you have not gone completely through menopause; or

  • you are pregnant.

Femara is for use only in women who can no longer get pregnant. Letrozole can harm an unborn baby. Do not use letrozole if you are pregnant. Use effective birth control if you are not past menopause. Keep using birth control for at least 3 weeks after your last dose of Femara. Tell your doctor if you think you may be pregnant.

To make sure this medicine is safe for you, tell your doctor if you have:

  • liver disease (especially cirrhosis);

  • osteoporosis, osteopenia (low bone mineral density);

  • high cholesterol; or

  • if you also take tamoxifen.

You should not breastfeed while you are using letrozole and for at least 3 weeks after your last dose.

How should I take Femara?

Femara is usually taken once per day, or once every other day. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

You may take this medicine with or without food.

While using Femara, you may need frequent medical tests and your bone mineral density may also need to be checked.

Store at room temperature away from moisture and heat.

Dosing information

Usual Adult Dose for Breast Cancer:

For use as first-line treatment of postmenopausal women with hormone receptor positive or hormone receptor unknown locally advanced or metastatic breast cancer. Femara is also indicated for the treatment of advanced breast cancer in postmenopausal women with disease progression following antiestrogen therapy: 2.5 mg tablet orally administered once a day without regard to meals.

In patients with advanced disease, Letrozole therapy should continue until tumor progression is evident.

Usual Adult Dose for Breast Cancer - Adjuvant:

For use as extended adjuvant treatment of early breast cancer in postmenopausal women who have received 5 years of adjuvant tamoxifen therapy: 2.5 mg tablet orally administered once a day without regard to meals.

The optimal duration of treatment with Femara is not known. Treatment should be discontinued if there is a tumor relapse.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What to avoid

Avoid driving or performing any hazardous activities until you know how this medicine will affect you. Your reactions could be impaired.

Femara side effects

Get emergency medical help if you have signs of an allergic reaction to Femara: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Common Femara side effects may include:

  • hot flashes, warmth or redness in your face or chest;

  • headache, dizziness, weakness;

  • bone pain, muscle or joint pain;

  • swelling, weight gain;

  • increased sweating; or

  • increased cholesterol in your blood.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Femara?

Other drugs may interact with letrozole, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

Popular FAQ

Most side effects of letrozole are mild and temporary, lasting only a few days or weeks until your body gets used to taking the medication. Some other side effects of letrozole take a few months to develop and tend to persist long term until you stop taking letrozole. The half-life of letrozole is 2 days, so once you stop taking letrozole, you might continue to experience side effects for about a week to 10 days after your last dose. Continue reading

When you stop taking letrozole, most persistent side effects should improve within a week or 10 days, and as long as you have taken it for at least 5 years, then letrozole should continue to reduce the risk of breast cancer coming back for many years after you stop taking it. Letrozole is usually taken for 5 years, may be recommended for up to 10 years depending on your individual circumstances. The American Society of Clinical Oncology (ASCO) recommends that 10 years should be the maximum duration of therapy, based on their 2019 clinical practice guideline update. Continue reading

You can take letrozole (Femara) in the morning or evening, but you should take it at about the same time each day. Taking it at the same time each day will help you to remember your dose. Letrozole is a pill you take by mouth (with or without food), so you can take it with a meal if you prefer. If you miss a dose, do not double your dose the next day. Continue reading

Letrozole is not chemotherapy, it is a type of hormone therapy that is used to treat people with breast cancer that is hormone receptor-positive. If your cancer is hormone receptor-negative, then letrozole will not be of any benefit. Traditional chemotherapy agents stop cancer cells from growing, dividing, and making more cells. Letrozole works by blocking the action of the enzyme aromatase, which prevents the body from converting androgens into estrogens. Estrogen is a hormone that causes estrogen receptor-positive (ER+) breast cancer to grow. Letrozole belongs to the class of medicines known as aromatase inhibitors. Continue reading

Although diabetes and blood sugar increases are not listed as a side effect of letrozole treatment, treatment with letrozole is associated with a significantly increased risk for high blood sugar levels and diabetes. An Israeli study that investigated 2,246 breast cancer survivors found that women treated with letrozole were 4.3 times more likely to develop diabetes than women not taking letrozole, although the number of women prescribed letrozole was small. Overall, women prescribed any sort of hormone treatment (either tamoxifen or an aromatase inhibitor such as letrozole) had a 2.5 times higher risk of diabetes. Continue reading

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Femara only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.