Letrozole | Side Effects, Dosage, Uses & More

Generic Name:

letrozole, Oral tablet

All Brands

  • Femara
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Highlights for letrozole

Oral tablet
1

Letrozole is an oral drug used to treat certain types of breast cancer. It’s only used in women who have gone through menopause (postmenopausal).

2

Letrozole shouldn’t be used in women who haven’t gone through menopause yet. If you become pregnant while taking letrozole, stop taking it right away and tell your doctor.

3

This drug is used to treat breast cancer in three ways. It’s used as an adjuvant (additional) treatment for early breast cancer, or as an extended adjuvant treatment for early breast cancer. It’s also used as a first- or second-line treatment for advanced breast cancer.

4

The recommended dose is one 2.5-mg tablet taken by mouth once per day.

5

The more common side effects include bone pain, hot flashes, back pain, nausea, joint swelling or pain, or muscle pain.

IMPORTANT INFORMATION

Pregnancy

You shouldn’t use this drug if you’re pregnant or plan to become pregnant. The tablets can’t be used in women who haven’t gone through menopause yet (premenopausal women). If you recently went through menopause, you still may be able to get pregnant. Ask your doctor about effective forms of birth control.

Tiredness and dizziness

This drug can cause fatigue and dizziness. Use caution when driving, using machinery, or performing similar activities that require alertness.

Bone thinning

This drug lowers estrogen in your body, which may cause your bones to become weak or thin. This could increase your risk of fractures and lead to osteoporosis. Your doctor will check your bone mineral density before you start and during treatment with this drug.

Drug features

This drug is a prescription drug. It is available as an oral tablet.

This drug is available in its generic form. It’s also available as a brand-name drug called Femara. Generic drugs usually cost less. In some cases they may not be available in every strength or form as the brand. Talk to your healthcare provider to see if the generic product will work for you.

This drug may be used with other drugs to treat breast cancer.

Why it's used

This drug is only used in postmenopausal women. It is not used in women who have not yet gone through menopause.

More Details

How it works

This drug belongs to a drug class called aromatase inhibitors. A class of drugs refers to medications that work similarly.

More Details

Why it's used

This drug is only used in postmenopausal women. It is not used in women who have not yet gone through menopause.

This drug can be used to treat early breast cancer. It may be used as an adjuvant (additional) treatment for hormone receptor-positive early breast cancer. Or it may be used as an extended adjuvant treatment for early breast cancer. In this case, it is used in women who have received 5 years of tamoxifen therapy.

This drug can also be used as a first- or second-line treatment for advanced breast cancer. In this case, it is used to treat hormone receptor-positive or unknown, locally advanced or metastatic breast cancer. This drug is also used to treat advanced breast cancer in women whose cancer has gotten worse after anti-estrogen therapy.

How it works

This drug belongs to a drug class called aromatase inhibitors. A class of drugs refers to medications that work similarly. They are often used to treat similar conditions.

In postmenopausal women, an enzyme found in liver, fat, muscle, and breast cancer cells increases your estrogen. Many breast cancer tumors grow when estrogen is present. This drug stops the enzyme from working. This lowers the amount of estrogen in your body.

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letrozole Side Effects

Oral tablet

Most Common Side Effects

The more common side effects that can occur with letrozole include:

  • bone pain

  • hot flashes

  • back pain

  • nausea

  • joint swelling or pain

  • shortness of breath

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious Side Effects

If you experience any of these serious side effects, call your doctor right away. If your symptoms are potentially life threatening or if you think you’re experiencing a medical emergency, call 9-1-1.

  • bone thinning or weakness (osteoporosis). Symptoms can include:

    • broken bones
    • pain
    • trouble with movement
  • higher cholesterol levels

Pharmacist's Advice
Healthline Pharmacist Editorial Team

This drug can cause tiredness and dizziness. Don’t drive, use machinery, or do other activities that require alertness until you know how the drug will affect you.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
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letrozole May Interact with Other Medications

Oral tablet

Letrozole can interact with other medications, herbs, or vitamins you might be taking. That’s why your doctor should manage all of your medications carefully. If you’re curious about how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Note: You can reduce your chances of drug interactions by having all of your prescriptions filled at the same pharmacy. That way, a pharmacist can check for possible drug interactions.

Medications that might interact with this drug

Other breast cancer drugs
  • tamoxifen

This drug can cause the amount of letrozole in your body to decrease. Letrozole and tamoxifen shouldn’t be taken together.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

People with liver disease

This drug is processed by your liver. If your liver isn’t working well, it may take longer for this drug to be cleared from your body. This drug can build up, which can lead to greater side effects. If you have severe liver disease, your doctor will reduce your dose.

Pregnant women

This drug is a category X pregnancy drug. Category X drugs should never be used during pregnancy.

Tell your doctor if you’re pregnant or plan to become pregnant. 

Women who are breast-feeding

This drug may pass into breast milk. It can cause serious effects in a breastfeeding child.

You and your doctor may need to decide if you’ll take this drug or breastfeed. 

Allergies

This drug can cause a severe allergic reaction. Symptoms can include:

  • trouble breathing
  • swelling of your throat or tongue
  • hives

If you have these symptoms, call your doctor right away. If they are severe, call 9-1-1 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction to it before. Taking it a second time after an allergic reaction could be fatal.

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How to Take letrozole (Dosage)

Oral tablet

All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What are you taking this medication for?

Breast cancer

Brand: Femara

Form: Oral tablet
Strengths: 2.5 mg

Generic: letrozole

Form: Oral tablet
Strengths: 2.5 mg
Adult dosage (ages 18 years and older)

One 2.5-mg tablet taken by mouth once per day.

Child dosage (ages 0–17 years)

This medication hasn’t been studied in children. It shouldn’t be used in people younger than 18 years.

Special considerations

Liver disease: If you have severe liver disease, your doctor will reduce your dose by 50%. You’ll take 2.5 mg by mouth every other day.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Healthline Pharmacist Editorial Team

This drug comes with serious risks if you don’t take it as prescribed.

If you stop taking the drug suddenly or don’t take it at all

If you don’t take this drug on schedule, your breast cancer may come back.

If you miss doses or don’t take the drug on schedule

Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

If you take too much

You could have dangerous levels of the drug in your body. If you take too much of this drug, you are at higher risk of having the more common side effects, such as:

  • loss of control of body movements
  • decreased blood pressure
  • abnormal heart rhythms
  • shortness of breath

If you think you’ve taken too much of the drug, act right away. Call your doctor or local Poison Control Center, or go to the nearest emergency room.

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

Your doctor will do tests to tell if this drug is working. If this drug is working, your breast cancer growth will slow down or stop.

This drug is a long-term drug treatment.

When used to treat early breast cancer, the expected length of treatment is 5 years.

Important considerations for taking this drug

This drug must be stored at the right temperature

  • This medication should be stored at a temperature between 59°F (15°C) and 86°F (30°C).
  • Don’t freeze this drug.
  • Keep the drug away from light.
  • Keep your drugs away from areas where they could get wet, such as bathrooms. Store this drug away from moisture and damp locations.

Travel

When traveling with your medication:

  • Always carry your medication with you, such as in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t hurt this medication.
  • You may need to show airport staff your pharmacy’s label to clearly identify the medication. Keep the original pharmacy label with you.
  • Don’t leave this drug in the car, especially when the temperature is hot or freezing.

Clinical monitoring

Before starting and during your treatment with this drug, your doctor will monitor your:

  • cholesterol levels
  • liver function
  • bone density
  • breast cancer growth to see if it has decreased or stopped

Insurance

Many insurance companies require a prior authorization for this drug. This means your doctor will need to get approval from your insurance company before your insurance company will pay for the prescription.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

What does the pill look like?

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How Much Does letrozole Cost?

Oral tablet

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These prices represent the lowest priced national pharmacies for letrozole on GoodRx. They may be lower than your insurance.

Show Sources

  • Breckenridge Pharmaceutical Inc. (2011, March). Letrozole. Boca Raton, FL.
  • Novartis Pharmaceuticals Corporation. (2014, January). Femara- letrozole. East Hanover, NJ.

Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on August 20, 2015

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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