Letrozole (Femara): What to Expect, Side Effects, and More

If you’ve been diagnosed with hormone receptor-positive breast cancer and you’ve experienced menopause, your doctor may prescribe you the aromatase inhibitor letrozole. This medicine is used:

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  to reduce the risk of hormone receptor-positive, early-stage breast cancer coming back (recurring) 

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  to slow or stop the growth of advanced-stage, hormone receptor-positive breast cancer

Letrozole isn’t commonly used to treat pre-menopausal women and the medicine can’t be taken at the same time as tamoxifen.

See letrozole prescribing information.

Letrozole works by blocking the enzyme aromatase, which turns the hormone androgen into small amounts of estrogen in the body. This means less estrogen is available to stimulate the growth of hormone receptor-positive breast cancer cells.

Letrozole is a pill taken once per day. 

If you’ve been diagnosed with early-stage, hormone receptor-positive breast cancer, you could take letrozole in one of two ways:

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  as your first hormonal therapy medicine after breast cancer surgery; in this case, you’ll take letrozole for five years, although you may be advised to take the medicine for ten years in some cases

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  as your  second hormonal therapy medicine after five years of tamoxifen; in this case, you’ll also take letrozole for five years, for a total of 10 years of hormonal therapy

If you’ve been diagnosed with advanced-stage, hormone receptor-positive breast cancer, you’ll take letrozole as long as you’re getting benefits from the medicine. In this case, letrozole may be prescribed along with other medications.

If you have cirrhosis or other liver problems, letrozole may affect you more than people without liver problems. Your doctor will likely recommend that you take a lower dose of letrozole.

You shouldn’t take letrozole if you are pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. This is because letrozole may cause damage to a developing fetus. You should use an effective non-hormonal type of birth control while you are taking letrozole. Ask your doctor which type of non-hormonal birth control would be best for you. You should use the birth control for at least three weeks after your last dose of letrozole.

Like almost all breast cancer medicines, letrozole can cause side effects, some of them severe.

The most common side effects of letrozole are:

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  hot flashes

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  joint and bone pain

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  flushing

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  weakness

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  swelling

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  headache

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  dizziness

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  fatigue

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  high cholesterol

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  excess sweating

One potentially serious side effect of letrozole may be bone loss. Because letrozole lowers the amount of estrogen in the body, less estrogen reaches bone cells, which can lead to bone thinning and weakening and a higher-than-average risk of breaking a bone. If you’ve been diagnosed with osteopenia or osteoporosis, your doctor will likely monitor your bone density while you’re taking letrozole.

If you’re considering refusing or stopping letrozole or another hormonal therapy medicine because of side effects, talk to your doctor right away. There are steps you can take to ease some of the most common side effects.

Members of our community discuss their experiences with letrozole (Femara) in the community forum. Here are some of their comments. Remember, it's essential to talk to your doctor about any side effects you're having and ask about ways to manage them.

“I have only been taking Femara a week and I am having extremely vivid dreams. So far no bad ones but they are tiresome just the same. Most of the time I forget my dreams but with these I remember every little detail.” — tinharhall

“I’m on my third year of Femara and am tolerating it well. I categorize my side effects as ‘inconsistent and somewhat annoying.’ For example; I have sporadic instances of calf and arch cramps; intense sweating, joint pain and stiffness  — but never all at once and not day after day. My side effects come and they go, and blessedly, they are not severe.” —sarahsmilesatme

“I have been on Femara for one year now and have experienced joint pain, back pain, and difficulty walking … Now the hair loss.” — hockeynut

Read more in our letrozole discussion forum.

The cost of letrozole may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use. 

Note: Your insurance company may require you to get prior authorization before covering letrozole. 

If your doctor prescribes letrozole and you have problems paying for it or getting it covered by insurance, the Novartis Oncology Patient Support program may be able to help you.

Learn more about financial assistance and medicine cost-lowering tips.