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Trade/other name(s): Femara

Why would this drug be used?

Letrozole is used to treat breast cancer in women who have already gone through menopause and no longer have menstrual periods (postmenopausal women )

How does this drug work?

Letrozole belongs to a general group of drugs called aromatase inhibitors. It keeps the body from making estrogen without affecting other hormones. Cancer cells that need estrogen are stopped from growing.

Before taking this medicine

Tell your doctor…

  • If you are allergic to anything, including medicines, dyes, additives, or foods.
  • If you think you might want to have children in the future. This drug has only been tested in women who have gone through menopause, and it may reduce fertility in those who have not. It may also reduce fertility if used in men. Talk with your doctor about the possible risk with this drug and options that may preserve your ability to have children.
  • If you are pregnant, trying to get pregnant, or if there is any chance of pregnancy. There may be an increased risk of harm to the fetus if a woman takes this drug during pregnancy.
  • If you are breast-feeding. It is not known whether this drug passes into breast milk. If it does, it could harm the baby.
  • About any other prescription or over-the-counter medicines you are taking, including vitamins and herbs. In fact, keeping a written list of each of these medicines (including the doses of each and when you take them) with you in case of emergency may help prevent complications if you get sick.

Interactions with other drugs

If tamoxifen is given with letrozole, it lowers the letrozole level in the blood.

Check with your doctor, nurse, or pharmacist about other medicines, vitamins, herbs, and supplements, and whether alcohol can cause problems with this medicine.

Interactions with foods

No serious interactions with food are known at this time. Check with your doctor, nurse, or pharmacist about whether foods may be a problem.

Tell all the doctors, dentists, nurses, and pharmacists you visit that you are taking this drug.

How is this drug taken or given?

Letrozole is a pill taken by mouth once a day. The dose is usually the same for all adults. Take with water, with or without food. Take this drug exactly as directed by your doctor. If you do not understand the instructions, ask your doctor or nurse to explain them to you.

Keep the medicine in a tightly closed container away from heat and moisture and out of the reach of children and pets.


Some people feel dizzy and tired when taking this drug, and a few notice feeling sleepy. This may affect driving. Find out how it affects you before driving or operating other dangerous machinery.

It is important to keep taking this drug, even if you feel well. If you are bothered by side effects, talk to your doctor or nurse to find out if the problems are serious. Many side effects can be managed with help from your doctor.

Possible side effects

You will probably not have most of the following side effects, but if you have any talk to your doctor or nurse. They can help you understand the side effects and cope with them.


  • pain in bones, joints, or muscles

Less common

  • headache
  • tiredness (fatigue)
  • nausea
  • swelling, usually of arms, legs, or feet
  • rashes
  • increased osteoporosis (thinning bones)


  • hot flashes
  • vomiting
  • loss of appetite
  • diarrhea
  • constipation
  • chest pain
  • higher cholesterol levels in the blood
  • allergic reaction with swelling mouth or throat, skin welts, or trouble breathing

*See "Precautions" section for more detailed information.

Other side effects not listed above can also occur in some patients. Tell your doctor or nurse if you develop these or any other problems.

FDA approval

Yes – first approved in 1997.

Disclaimer: This information does not cover all possible uses, actions, precautions, side effects, or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for talking with your doctor, who is familiar with your medical needs.

Last Medical Review: 12/02/2009
Last Revised: 12/02/2009