Letrozole

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: May 21, 2024

Warnings

Letrozole (Femara) Risks, Warnings, and Complications

Letrozole can cause or worsen health problems in some people. Talk to your doctor or pharmacist about other treatments for breast cancer if you are at an increased risk of complications from this drug. Some of the risks of letrozole use include:

WEAK BONES: Letrozole can cause a decrease in bone mineral density, leading to weakened bones and an increased risk of fractures. Your healthcare provider may order a bone mineral density (BMD) test before starting this medicine and during letrozole therapy. If you have low bone mineral density, your provider may prescribe medications to improve your bone quality. Tell your doctor without delay if you develop bone pain while on this medicine.
HIGH CHOLESTEROL: Some people taking Femara (letrozole) develop high cholesterol. If diet and exercise are not enough to keep your cholesterol levels in check, your healthcare professional may prescribe cholesterol-lowering medication.
LIVER PROBLEMS: Letrozole is broken down by the liver in the body. In people with impaired liver function, high levels of letrozole can build up in the body and increase the risk of severe side effects. Your healthcare provider may prescribe a lower dose of letrozole if you have liver problems.
CAUTION WHILE DRIVING: Letrozole can cause tiredness, weakness, sleepiness, dizziness, and blurred vision. These side effects can put you at risk of injuries and accidents. Be careful while driving a motor vehicle or operating machinery until you know how letrozole affects you.
HARM TO AN UNBORN BABY: Taking letrozole during pregnancy can cause harm to the unborn baby, including spontaneous abortion and congenital birth defects. Your healthcare provider may do a pregnancy test before starting treatment with letrozole. If you are sexually active, they may ask you to use appropriate contraception while you are on letrozole and for 3 weeks after the last dose.

Precautions Before Starting Letrozole (Femara)

Tell your doctor if you have ever had an allergic reaction to letrozole, any of the active or inactive ingredients in letrozole tablets, or any other drugs. Your pharmacy can give you a list of ingredients.

Give your doctor and pharmacist a complete list of your medications, including prescription drugs, over-the-counter medicines, dietary supplements, and herbal products. This can help avoid potentially dangerous interactions between your medications.

Give your doctor a complete medical history. Letrozole may not be safe for people with certain medical conditions, such as liver disease, osteoporosis, and high cholesterol.

Letrozole is used to treat breast cancer in postmenopausal women (women who have stopped getting their menstrual cycle and cannot get pregnant). Nonetheless, before starting treatment with this cancer drug, tell your doctor if you are pregnant or nursing an infant with breast milk. Letrozole can be harmful to the fetus if taken during pregnancy.

Precautions During Use of Letrozole (Femara)

Keep all your medical and lab appointments while on letrozole.

Letrozole can make you drowsy, dizzy, sleepy, and tired. Only drive, operate machinery, or do other potentially dangerous activities once you know how it affects you.

Call your doctor immediately if you become pregnant while on letrozole.

Tell all your doctors you are on letrozole, especially before any surgical procedure, including dental treatments.

Letrozole (Femara) Drug Interactions

Taking letrozole with certain other drugs can affect how the medications work. Interactions between letrozole and other medications can lead to severe side effects. The following medications can interact with letrozole:

Estrogen-containing medications such as hormone replacement therapy (HRT) and hormonal contraceptives (birth control pills, patches, injections, and rings)
Raloxifene (Evista)
Cancer treatments like tamoxifen (Nolvadex)

The above list does not include all the possible interactions of letrozole. Give your doctor or pharmacist a complete list of your medications, including prescription drugs, over-the-counter medications, dietary supplements, and herbal remedies. Also, tell your healthcare professional if you smoke, drink alcohol, or use recreational drugs because some of these substances can cause serious health complications when used with prescription medications.

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