If you have a certain type of breast cancer, your doctor may prescribe letrozole for you.

It’s prescribed for adult females* who’ve gone through menopause. It’s used to treat certain forms of:

  • early breast cancer (breast cancer that hasn’t spread beyond your breast or lymph nodes in your armpits)
  • locally advanced breast cancer (breast cancer that’s spread to areas near your breast or in the lymph nodes in your armpit)
  • metastatic breast cancer (breast cancer that’s spread to areas beyond those near your breast or in the lymph nodes in your armpit)

In some cases, letrozole can be used by itself. But it can also be used as add-on treatment following surgery, or together with other drugs.

To learn more about these conditions and how letrozole treats them, see the “What are letrozole oral tablets used for?” section below.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Letrozole oral tablets basics

Letrozole is an active drug ingredient that’s available as a generic medication. It comes as oral tablets that you’ll swallow.

Letrozole is a hormone therapy for breast cancer.

Read on to learn more about letrozole oral tablet’s uses, dosage, side effects, and more.

Letrozole oral tablets brand-name versions

Letrozole oral tablets are the generic version of the brand-name drug Femara.

Letrozole oral tablets are a generic drug, which means they’re an exact copy of the active drug in a brand-name medication. The brand-name medication that letrozole oral tablets are based on is called Femara.

Generic drugs are thought to be as safe and effective as the brand-name drug they’re based on. In general, generics usually cost less than brand-name drugs do.

If you’d like to know more about using Femara instead of letrozole oral tablets, talk with your doctor. Check out this article to learn more about the differences between generic and brand-name drugs.

Like most drugs, letrozole oral tablets may cause mild or serious side effects. The lists below describe some of the more common side effects that letrozole oral tablets may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you may be taking

Your doctor or pharmacist can tell you more about the potential side effects of letrozole oral tablets. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a short list of some of the mild side effects that letrozole oral tablets can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read letrozole oral tablets’ prescribing information.

Mild side effects of letrozole oral tablets that have been reported include:

  • hot flashes
  • feeling weak or having increased tiredness
  • dizziness
  • belly pain or cramping
  • hair loss
  • swelling, usually in your arms, feet, hands, or legs
  • sweating more than usual
  • vaginal spotting
  • weight gain*
  • bone, muscle, or joint pain*
  • headache*

* For more information about this side effect, see the “Side effect focus” section below.

Mild side effects of many drugs may go away within a few days or a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

Serious side effects

Serious side effects from letrozole oral tablets can occur, but they aren’t common. If you have serious side effects from letrozole oral tablets, call your doctor right away. But if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of letrozole oral tablets that have been reported include:

* For more information about this side effect, see the “Side effect focus” section below.

How long before letrozole’s side effects start and how long they last

Letrozole starts working right away in your body after you begin taking it. This means you can also have side effects from it right away.

You may have some side effects very quickly. These include side effects such as flushing, hot flashes, or headaches.

Other side effects may take longer to develop because they require a build-up of the drug in your body. These could include weakened bones, for example.

Usually, side effects from letrozole will be reduced after the first few months of treatment.

Side effect focus

Learn more about some of the side effects letrozole oral tablets may cause.

Weight gain

Letrozole may cause weight gain. In fact, this was a common side effect in studies of letrozole.

You may also experience weight gain with letrozole if you have swelling, which is another possible side effect of the drug. Swelling from letrozole usually occurs in your arms, feet, hands, or legs.

What might help

If you’re concerned about gaining weight while taking letrozole, talk with your doctor.

They can suggest ways to help you manage a healthy body weight. Additionally, you can find information about weight management here.

Headache

During studies of letrozole, headaches were a common side effect in people taking the drug.

What might help

To help relieve headaches with letrozole, you can take over-the-counter (OTC) medications. These include acetaminophen (Tylenol) and ibuprofen (Advil).

But before starting any new medications, be sure to talk with your doctor or pharmacist. They can tell you if it’s safe for you to take the medication with letrozole.

Also, you can apply an ice pack or heat pad to your head to help ease the headache. Holding the ice pack or heating pad on your head for about 10 minutes a few times a day when you’re having a headache is recommended.

For other home remedies for quick headache relief, check out this article.

Joint pain

In studies, joint pain was a common side effect of letrozole. Letrozole and other drugs in the same group of medications commonly cause joint pain and stiffness.

What might help

Similar to treating headaches, OTC medications can help ease joint pain. Examples of OTC medications include acetaminophen (Tylenol) and ibuprofen (Advil).

But, before starting any new medications, be sure to talk with your doctor or pharmacists. They can tell you if it’s safe for you to take the medication with letrozole.

Additionally, walking can help strengthen your muscles and protect your joints from pain.

If your joint pain doesn’t get better, talk with your doctor. They may recommend ways to help reduce the pain.

Allergic reaction

An allergic reaction to letrozole oral tablets wasn’t reported in studies of the drug. But it can still happen.

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include swelling under your skin, typically in your eyelids, lips, hands, or feet. They can also include swelling of your tongue, mouth, or throat, which can cause trouble breathing.

Call your doctor right away if you have an allergic reaction to letrozole oral tablets. But if you think you’re having a medical emergency, call 911 or your local emergency number.

Letrozole is sometimes used off-label to treat infertility in females.* Off-label use is when a drug that’s approved to treat one condition is used to treat another condition.

Letrozole stops your body from making the hormone estrogen. Estrogen typically prevents your ovaries from ovulating (releasing an egg). When estrogen isn’t being made, your body can ovulate. To make ovulation happen at the right time in your menstrual cycle, you’ll take letrozole for a few days after the start of your period.

Letrozole is often used to treat infertility that’s caused by polycystic ovarian syndrome (PCOS). But it can treat other forms of infertility, as well. (PCOS affects normal ovulation, and it’s one of the more common causes of infertility in females.)

If you’re taking letrozole to induce ovulation, using intrauterine insemination (IUI) may help you become pregnant better than having timed sex will. (IUI is a procedure in which a sample of sperm is placed directly into the uterus.)

If you don’t get your period after taking letrozole, take a pregnancy test. Let your doctor know about your missed period and your test results.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Letrozole dosage for infertility

You may have specific questions about using letrozole for infertility, such as:

  • What’s the dosage of letrozole for infertility?
  • When will you ovulate after taking letrozole?
  • How many cycles of letrozole are needed to get pregnant?

Because this isn’t an approved use for letrozole, the manufacturer of the drug doesn’t provide dosage guidelines for infertility treatment. So, check with yourdoctor about the dosage of letrozole for infertility that’s recommended for you. They can also answer other questions related to using this drug for infertility.

Letrozole vs. Clomid and metformin

Letrozole is an active drug, while Clomid was a brand-name medication that contained the active drug clomiphene. Clomid is no longer available, but its generic version, clomiphene, is still available.

Both letrozole and clomiphene are used to treat infertility in females by helping to cause ovulation. Unlike letrozole, clomiphene is approved for this use.

Metformin is a drug that’s typically used to treat diabetes. But it’s also sometimes prescribed to help treat other PCOS-related conditions, such as elevated blood sugar levels and insulin resistance. Studies haven’t shown metformin to be useful when used by itself for infertility. But sometimes, metformin is given together with clomiphene to help treat infertility in females* with PCOS.

If you want to know more about the different treatment options for infertility, talk with your doctor.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Find answers to some commonly asked questions about letrozole oral tablets.

Is letrozole a chemotherapy drug? How does it work and what’s its half-life?

Letrozole isn’t a chemotherapy drug. Instead, it’s a type of hormone therapy. Specifically, it’s called an aromatase inhibitor.

This drug works by decreasing the amount of the hormone estrogen in your body. Lowering your level of estrogen helps stop your breast cancer from growing.

Chemotherapy drugs are also a type of cancer treatment. They work by killing cells in your body that quickly multiply (make more cells). This includes cancer cells.

But both cancer cells and healthy cells in your body can quickly multiply. This is why chemotherapy can cause hair loss and many other side effects.

Letrozole’s half-life is about 2 days. This means it takes about 2 days for your body to clear half a dose of the drug. In general, a drug is mostly cleared from your body after four to five half-lives.

Does letrozole cause teeth-related side effects?

Teeth-related side effects weren’t reported with letrozole use during studies.

Letrozole can cause bone pain and joint pain. If these affect your jaw, it’s possible the pain could spread and feel like tooth pain.

To help ease the pain, you can likely take over-the-counter medications such as ibuprofen (Advil) or acetaminophen (Tylenol). But check with your doctor before taking any medications with letrozole.

If you’re having severe tooth or jaw pain, call your doctor and ask them about treatment options.

Are there any foods to avoid while I’m taking letrozole?

No, there aren’t any specific foods you should avoid while you’re taking letrozole.

Food doesn’t interact with letrozole. But it can impact some of side effects of the drug. For instance, if you have hot flashes or nausea with letrozole, you can try reducing the amount of spicy or rich foods you eat. Doing so may help lessen your discomfort.

If you have concerns about eating certain foods with letrozole, talk with your doctor.

Can letrozole be used for bodybuilding, PCT, or endometriosis?

Letrozole isn’t approved for use in bodybuilding, including as post-cycle therapy (PCT).

PCT is used to help minimize side effects that bodybuilders have when they take anabolic steroids to build muscles. This includes the side effect hypogonadism (a condition in which the body doesn’t produce many, or any, sex hormones.)

The World Anti-Doping Agency prohibits athletes in competitive sports from using letrozole for non-approved uses. So, if your doctor prescribes letrozole for medical uses, you should not take it for other purposes such as bodybuilding or PCT.

Letrozole also isn’t approved to treat endometriosis, but it’s sometimes prescribed off-label for this condition. (Off-label use is when a drug that’s approved to treat one condition is used to treat another condition.) Endometriosis can cause pelvic pain, irregular periods, and trouble getting pregnant.

Usually, letrozole is prescribed for endometriosis after other treatments haven’t worked. And it’s often prescribed together with a form of the hormone progestin. Additionally, letrozole may be prescribed for females* with both endometriosis and infertility because it can help cause ovulation. (When you ovulate, an egg is released from your ovaries).

If you have questions about using letrozole in bodybuilding or for endometriosis, talk with your doctor.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

How does letrozole compare with tamoxifen?

Letrozole and tamoxifen are both used to treat breast cancer. They work by reducing the amount of the hormone estrogen in your body. These drugs are both forms of hormone therapy for breast cancer.

Letrozole is the generic version of the brand-name drug Femara. Tamoxifen is an active drug that’s available only as a generic drug. It’s not available as a brand-name medication.

In some cases, letrozole is prescribed for early breast cancer that’s already been treated with surgery plus 5 years of tamoxifen therapy. (With early breast cancer, the cancer hasn’t spread beyond your breast or lymph nodes in your armpits.)

Letrozole can interact with tamoxifen. So, it’s recommended that you don’t take the drugs at the same time. With this interaction, tamoxifen can reduce how well letrozole works.

Talk with your doctor if you have more questions about the differences and similarities between letrozole and tamoxifen.

Will stopping letrozole cause withdrawal symptoms?

Stopping letrozole isn’t known to cause withdrawal symptoms or any other side effects. So, letrozole doesn’t need to be gradually stopped. But be sure to talk with your doctor before stopping this drug.

In certain situations, if letrozole has stopped working for you, your doctor may have you stop taking it in order to cause a “withdrawal response.”

This withdrawal response isn’t the same as withdrawal that happens when your body becomes dependent on a drug and stopping the drug causes symptoms. (With dependence, your body needs the drug for you to feel normal.) Instead, this response is a shift in your hormone levels that happens when you stop taking letrozole.

This treatment approach isn’t right for everyone. But your doctor will recommend if it’s something you should do.

If you doctor thinks letrozole has stopped working for you, talk with them about whether stopping the drug could be beneficial for you.

Your doctor will explain how you should take letrozole oral tablets. They’ll also explain how much to take and how often. Be sure to follow your doctor’s instructions. Below are commonly used dosages, but always take the dosage your doctor prescribes.

Taking letrozole oral tablets

Letrozole comes as oral tablets that you’ll take by mouth.

It’s only available in one strength: 2.5 milligrams (mg).

Dosage

For breast cancer, you’ll take one letrozole oral tablet once daily. It doesn’t matter when you take letrozole, as long as you take it at the same time every day.

Taking letrozole oral tablets with other drugs

Letrozole may be used with other therapies in your breast cancer treatment plan.

For instance, your doctor may prescribe other breast cancer treatments, such as fulvestrant, in addition to letrozole.

Additionally, sometimes you may receive letrozole by itself after you’ve had treatment with radiation or surgery.

Sometimes, you may be prescribed letrozole after you’ve taken tamoxifen for 5 years. Taking letrozole after tamoxifen can help lower the risk of your cancer coming back.

If you have questions about taking letrozole with other drugs, talk with your doctor.

Questions about taking letrozole oral tablets

Here’s a list of common questions related to taking letrozole.

  • What if I miss a dose of letrozole oral tablets? If you miss a dose of letrozole, take your missed dose as soon as you remember. If it’s almost time for your next usual dose, skip the missed dose and take the next dose at the regular time. If you don’t know if you should take or skip a missed dose, talk with your doctor or pharmacist.
  • Will I need to use letrozole oral tablets long term? Letrozole is meant to be used as long-term treatment for breast cancer. If your breast cancer gets worse or if you can’t tolerate the side effects of letrozole, your doctor may have you stop taking it. Most people take letrozole for at least 5 years.
  • Can letrozole oral tablets be chewed, crushed, or split? No, you should not chew, crush, or split letrozole tablets. When taking letrozole tablets, swallow them whole. If you have trouble swallowing a whole tablet, talk with your doctor or pharmacist.
  • Should I take letrozole oral tablets with food? Letrozole can be taken with or without food.
  • How long do letrozole oral tablets take to work? Once you take letrozole, it starts working right away to treat your breast cancer. But even though it starts working right away, you won’t notice it working. Your doctor will monitor your condition to make sure that letrozole is working for you.
Questions for your doctor

You may have questions about letrozole oral tablets and your treatment plan. It’s important to discuss all your concerns with your doctor.

Here are a few tips that might help guide your discussion:

  • Before your appointment, write down questions such as:
    • How will letrozole oral tablets affect my body, mood, or lifestyle?
  • Bring someone with you to your appointment if doing so will help you feel more comfortable.
  • If you don’t understand something related to your condition or treatment, ask your doctor to explain it to you.

Remember, your doctor and other healthcare professionals are available to help you. They want you to get the best care possible. So, don’t be afraid to ask questions or offer feedback on your treatment.

Before taking letrozole, talk with your doctor about your overall health and any other medical conditions you have.

These and other important considerations are discussed in detail below.

Interactions

Taking medications, vaccines, foods, and other things with a certain drug can affect how the drug works. These effects are called interactions.

Before taking letrozole oral tablets, be sure to tell your doctor about all medications you take, including prescription and over-the-counter types. Also describe any vitamins, herbs, or supplements you use. Your doctor or pharmacist can tell you about any interactions these items may cause with letrozole oral tablets.

Interactions with drugs or supplements

Letrozole oral tablets can interact with several types of drugs. These drugs include:

This list doesn’t contain all types of drugs that may interact with letrozole oral tablets. Your doctor or pharmacist can tell you more about these interactions and any others that may occur with use of letrozole oral tablets.

Warnings

Letrozole oral tablets may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you take letrozole oral tablets. Factors to consider include those in the list below.

  • High cholesterol. Letrozole can cause high cholesterol. Before starting letrozole, tell your doctor if you have high cholesterol. While you’re taking letrozole, your doctor will check your cholesterol levels with certain blood tests. If your levels get too high, your doctor may prescribe a medication to lower them, such as atorvastatin (Lipitor) or rosuvastatin (Crestor).
  • Allergic reaction. If you’ve had an allergic reaction to letrozole oral tablets or any of its ingredients, you shouldn’t take the medication. Ask your doctor what other medications are better options for you.
  • Liver problems. Before starting letrozole, let your doctor know if you have any liver problems, such as cirrhosis. If you have liver problems, the level of letrozole in your body can be increased. But this increases your risk for side effects from the drug. If you have liver problems, your doctor may prescribe a lower dose of letrozole than usual for you.
  • Osteoporosis. Before you start taking letrozole, let your doctor know if you have osteoporosis. Letrozole can cause weakened bones, which occur with osteoporosis. So, while you’re taking letrozole, your doctor may monitor your bones with a bone mineral density test. This test checks the strength of your bones. If your bones are weak, your doctor may prescribe other drugs to help protect them while you’re taking letrozole.

Letrozole oral tablets and alcohol

Alcohol isn’t known to interact with letrozole. But, alcohol can cause side effects similar to those of letrozole.

If you drink alcohol while you’re taking letrozole, you might be more likely to have certain side effects, including:

If you plan to drink alcohol while you’re taking letrozole, make sure to talk with your doctor. They can recommend if there’s an amount that’s safe for you.

Pregnancy and breastfeeding

You shouldn’t take letrozole while you’re pregnant or breastfeeding. You should also avoid becoming pregnant or breastfeeding for at least 3 weeks after your last dose of the drug.

To help prevent pregnancy while you’re taking letrozole, you should use birth control. You should also continue to use birth control for at least 3 weeks after you stop treatment.

If you’re pregnant or considering pregnancy, talk with your doctor before you start taking letrozole. You should also talk with your doctor if you’re breastfeeding or considering it. Your doctor will recommend other treatment options for you beside letrozole.

Costs of prescription drugs can vary depending on many factors. These factors include what your insurance plan covers and which pharmacy you use. To find current prices for letrozole oral tablets in your area, visit GoodRx.com.

Financial assistance to help you pay for letrozole oral tablets may be available. Medicine Assistance Tool and NeedyMeds are two websites that provide resources to help reduce the cost of letrozole oral tablets.

These websites also offer tools to help you find low-cost healthcare and certain educational resources. To learn more, visit their websites.

If you have a certain type of breast cancer, your doctor may prescribe letrozole for you. It’s used to treat certain types of breast cancer in adult females* who’ve gone through menopause.

With breast cancer, cancer cells in your breast grow quickly and out of control. This rapid growth of cells can cause a tumor to form in your breast. The cells may even spread to other parts of your body.

Letrozole is used to treat the following types of breast cancer:

  • Early breast cancer that’s hormone receptor-positive (HR+). With early breast cancer, the cancer hasn’t spread beyond your breast or lymph nodes in your armpits. HR+ breast cancer means the cancer has receptors (attachment sites) for certain hormones and its growth is caused by the hormones. For this use, letrozole helps lower the risk of the cancer returning after it’s been removed with surgery.
  • Early breast cancer that’s already been treated with surgery and tamoxifen. For this use, letrozole is given after tamoxifen, which is another breast cancer drug. Tamoxifen is typically prescribed for at least 5 years before letrozole is prescribed. In this case, letrozole helps lower the risk of the cancer returning.
  • Advanced breast cancer that’s HR+ or HR-unknown. Advanced breast cancer includes both locally advanced and metastatic breast cancer. With locally advanced breast cancer the cancer has spread to areas in the body that are close to the breast or lymph nodes in your armpit. With metastatic breast cancer, the cancer has spread to further areas, beyond those close to your breast or lymph nodes in your armpits. Cancer that’s HR-unknown means the cancer hasn’t been tested yet to know whether it’s HR+ or HR-negative (HR-). For this use, letrozole helps prevent your cancer from spreading further in your body.
  • Advanced breast cancer that has spread following certain treatments. For this purpose, letrozole is given after breast cancer has been treated with another breast cancer medication. Specifically, it’s given after a drug that blocks the hormone estrogen has been tried. In this case, letrozole helps prevent your cancer from spreading further in your body.

Letrozole decreases the amount of estrogen in your body. Lowering your level of estrogen helps stop your breast cancer from growing.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Letrozole and anastrozole (Arimidex) are both used to help treat certain types of breast cancer. They’re used in females* who’ve gone through menopause.

Both medications belong to a group of drugs called aromatase inhibitors. They work by decreasing the amount of the hormone estrogen in your body. This helps stop your breast cancer from growing.

If you’d like more information about letrozole compares with Arimidex, see this detailed breakdown. Check with your doctor to find out which drug is right for you.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Don’t take more letrozole oral tablets than your doctor prescribes. Using more than this can lead to serious side effects.

What to do in case you take too much letrozole

Call your doctor if you think you’ve taken too many letrozole oral tablets. You can also call 800-222-1222 to reach the American Association of Poison Control Centers, or use its online resource. If you have severe symptoms, immediately call 911 (or your local emergency number) or go to the nearest emergency room.

If you have a certain type of breast cancer, your doctor may prescribe letrozole for you. To learn about the cancers letrozole treats, see the “What are letrozole oral tablets used for?” section above.

Talk with your doctor if you have questions about taking this drug for breast cancer. Here are a few questions you may want to ask:

  • Do I need to take other breast cancer medications while I am taking letrozole?
  • Will any of my current medications interact with letrozole?
  • Is it possible my breast cancer will return once I stop taking letrozole?

If you want to ask about other treatment options, this article about breast cancer treatment options may be helpful to you.

Additionally, you can sign up for Healthline’s breast cancer newsletter to:

  • learn about breast cancer detection and diagnosis
  • find out about possible treatments for breast cancer
  • read inspiring first-person stories and informative Q&As from doctors

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 another 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.