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Uses

What is letrozole used for?

Letrozole is commonly used to treat certain types of breast cancer, including hormone receptor-positive breast cancer, in women after menopause.

Letrozole may also be used for other conditions as determined by your healthcare provider.

How does letrozole work (mechanism of action)?

Letrozole belongs to a class of medicines called  aromatase inhibitors. It works by blocking an enzyme called aromatase that helps produce estrogen in the body. By lowering the amount of estrogen, letrozole can help prevent the growth of tumors that rely on estrogen to grow.

How is letrozole supplied (dosage forms)?

Letrozole is available as Femara and generic letrozole in the following dosage form that is taken by mouth.

  • 2.5 mg oral tablets

How should I store letrozole?

Letrozole should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place.

Side Effects

What are the most common side effects of letrozole?

The most common side effects of letrozole are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

  • Hot flashes, flushing, or increased sweating
  • Lack of energy and weakness
  • Pain, including bone pain, headache, and joint pain
  • High cholesterol (see below)
  • Fluid retention
  • Dizziness

There may be other side effects of letrozole that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of letrozole?

While less common, the most serious side effects of letrozole are described below, along with what to do if they happen.

Severe Allergic Reactions. Letrozole may cause allergic reactions, which can be serious. Stop taking letrozole and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Weak Bones. Taking letrozole for a long time may cause your bones to become weaker, leading to reduced bone density (osteopenia). It may also cause a more serious condition called osteoporosis, which can cause bones to break (fracture) more easily. If you take letrozole, your healthcare provider may monitor your bone density. Tell your healthcare provider if you break a bone, and get a bone mineral density test if one is ordered for you.

High Cholesterol. Taking letrozole may cause levels of cholesterol (fat) in your blood to go up. If you take letrozole, your healthcare provider may monitor your cholesterol levels. Keep all appointments to have your blood cholesterol checked.

Warnings & Precautions

Who should not use letrozole?

Allergies to Ingredients. People who are allergic to any of the following should not take letrozole.

  • Letrozole
  • Femara
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific letrozole products they stock.

Pregnancy. Do not take letrozole if you are pregnant. If you become pregnant, contact your healthcare professional right away. See the Pregnancy section for more details.

What should I know about letrozole before using it?

Do not take letrozole unless it has been prescribed to you by a healthcare provider. Take it as prescribed.

Do not share letrozole with other people, even if they have the same condition as you. It may harm them.

Keep letrozole out of the reach of children.

Letrozole can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how letrozole affects you.

Letrozole may affect your ability to become pregnant or get a partner pregnant. Talk with your healthcare provider if you have any concerns.

Ask your healthcare provider about your vitamin D level. You may need to take a supplement.

What should I tell my healthcare provider before using letrozole?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if letrozole is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your healthcare provider if you have any of the following.

Other Medicines and Supplements. Letrozole may interact with other medicines and supplements. Before taking letrozole, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Do not take letrozole and tell your healthcare provider right away if you are pregnant or plan to become pregnant. Letrozole can cause harm to an unborn baby. A negative pregnancy test is necessary before starting treatment. If you can become pregnant, use effective birth control while you are taking letrozole and for at least 3 weeks after your last dose. Talk to your healthcare provider about your birth control options. Tell your healthcare provider right away if you have unprotected sex or if you think your birth control has failed.

Breastfeeding. Do not breastfeed during treatment with letrozole or for 3 weeks after your last dose. It is not known if letrozole passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed.

Interactions

Does letrozole interact with foods or drinks?

There are no known interactions between letrozole and foods or drinks.

It is unknown if drinking alcohol will affect letrozole. The risk of dizziness and sleepiness may be increased if you drink alcohol while taking letrozole.

Does letrozole interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking letrozole.

  • Tamoxifen, a medicine that is used to treat and prevent breast cancer
  • An estrogen medicine, such as hormone replacement, certain birth control pills, and estrogen creams, rings, or suppositories

This may not be a complete list of medicines that can interact with letrozole. Always check with your healthcare provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much letrozole?

If you or someone else has used too much letrozole, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of letrozole?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.