If you have a certain type of breast cancer, your doctor might suggest Femara (letrozole) as a treatment option.

Femara is a prescription drug used in adult females* who’ve gone through menopause. It’s used to treat the following types of cancer:

Femara comes as a tablet you take by mouth once per day. It’s meant to be taken as a long-term treatment.

For more information about Femara, including details about the types of breast cancer it treats, see this in-depth article on the drug.

Like other drugs, Femara can cause mild or serious side effects. Keep reading to learn more.

* 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.

Some people may experience mild or serious side effects during their Femara treatment. Examples of Femara’s commonly reported side effects include:

* To learn more about this side effect, see “Side effects explained” below.

Most side effects of Femara are mild. Examples of mild side effects that have been reported with this drug include:

* To learn more about this side effect, see “Side effects explained” below.

In most cases, these side effects should be temporary. And some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. And don’t stop taking Femara unless your doctor recommends it.

Femara may cause mild side effects other than the ones listed above. See Femara’s prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Femara, visit MedWatch.

Serious side effects are possible from taking Femara. Those that have been reported with Femara include:

To learn more about each of these side effects, see “Side effects explained” below.

If you develop serious side effects while taking Femara, call your doctor right away. If the side effects seem life threatening or if you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* An allergic reaction is possible after taking Femara. But this side effect wasn’t reported in studies.

Below you’ll find answers to some frequently asked questions about Femara’s side effects.

Will I have side effects after stopping my Femara treatment?

It’s possible that you may continue to have side effects from Femara even after you stop taking it.

Femara can stay in your system after you stop taking the drug. If you experienced side effects while taking Femara, those side effects may not go away for a few weeks after your last dose.

However, stopping Femara treatment isn’t known to cause new side effects. And the drug doesn’t need to be stopped gradually to prevent side effects from occurring.

Most people who use Femara take the drug for at least 5 years. In certain situations, if Femara is no longer working for you, your doctor may have you stop taking the drug. If you’re concerned about side effects you may experience when ending your Femara treatment, talk with your doctor.

Does Femara cause anxiety or depression?

Although they’re not common side effects, in some cases, Femara can cause anxiety or depression.

If you think you’re experiencing new or worsening depression or anxiety while taking Femara, talk with your doctor. They can help determine if you should keep taking Femara or switch to a different treatment.

How do the side effects of Femara and Arimidex compare?

Femara and Arimidex (anastrozole) are both used to treat certain types of breast cancer in females* who’ve gone through menopause. Both medications belong to a group of drugs called aromatase inhibitors. They work by lowering estrogen levels within your body, which helps stop the growth of breast cancer.

Because these drugs work in the same way, their side effects are very similar. But Arimidex does cause some additional side effects that don’t occur with Femara.

For details about how side effects for these drugs compare, see the “Arimidex vs. letrozole” section of this article. (Letrozole is the active drug in Femara.) You can also talk with your doctor or pharmacist to learn more.

* 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 long do Femara’s side effects typically last?

Mild side effects of Femara can usually go away within a few days or a couple weeks. But serious side effects are more likely to last longer. It’s possible that any side effect of Femara may last throughout your treatment. Some side effects, such as osteoporosis (weakened bones), will not get better on their own, even after you stop taking Femara.

How long side effects last can vary from person to person. If you experience side effects that don’t go way or interfere with your daily life, talk with your doctor or pharmacist.

Learn more about some of the side effects that Femara may cause.

Hair loss

Femara may cause hair loss in some people. But this was not one of the most common side effects reported in studies of the drug.

Femara is a type of hormone therapy used to treat breast cancer. It’s not chemotherapy, which is a type of cancer drug that most commonly causes hair loss.

What might help

If you’re concerned about hair loss while taking Femara, talk with your doctor. They may be able to suggest ways to help manage this side effect.

Weight gain

Some people taking Femara may experience weight gain. In studies, this was a common side effect reported in people taking the drug.

Swelling, another common side effect of Femara, can cause you to gain weight as your body holds on to water. Swelling caused by Femara typically occurs in your arms, feet, hands, or legs.

What might help

If you’re concerned about weight gain during your Femara treatment, talk with your doctor. They can recommend some ways to manage this side effect.

Weakened bones

Femara can decrease bone mineral density in some people. This can make your bones weaker and easier to break.

Your bones rely on estrogen to keep them strong. After menopause, your body produces less estrogen, which can weaken your bones. Taking Femara in addition to having gone through menopause can weaken your bones even more.

What might help

One way your doctor will monitor your bone strength is by measuring your bone mineral density. The greater the density, the stronger your bones are.

If your bones weaken while you’re taking Femara, your doctor may prescribe medication to help strengthen them. There are also some steps you can take to help strengthen your bones naturally.

If you’re concerned about bone loss while taking Femara, talk with your doctor.

High cholesterol

Taking Femara can cause high cholesterol in some people. In studies, increased cholesterol levels were one of the most common side effects among people taking Femara.

What might help

Your doctor will order blood tests to check your cholesterol levels before you begin taking Femara and during your treatment.

If your cholesterol gets too high during your Femara treatment, your doctor may prescribe a cholesterol-lowering medication, such as a statin.

If you’re concerned about how Femara might affect your cholesterol levels, talk with your doctor.

Fatigue

Femara may cause fatigue (lack of energy) in some people. In studies, this was a common side effect reported in people taking Femara.

What might help

If you experience fatigue during your Femara treatment that doesn’t go away or that’s bothersome, talk with your doctor. They may be able to suggest ways may help improve your energy level during your treatment.

Also, if you experience fatigue, extreme tiredness, or dizziness while taking Femara, you shouldn’t drive or operate heavy machinery. If you have questions about whether it’s safe for you to drive or operate machinery during your treatment, talk with your doctor or pharmacist.

Allergic reaction

Like most drugs, Femara can cause an allergic reaction in some people. But this side effect wasn’t reported in studies.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine), or a topical product, such as hydrocortisone cream, to manage your symptoms.

If your doctor confirms that you had a mild allergic reaction to Femara, they’ll decide if you should continue taking it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms that you had a serious allergic reaction to Femara, they may have you switch to a different treatment.

Keeping track of side effects

During your Femara treatment, consider keeping notes about any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dosage of the drug you were taking when you had the side effect
  • how soon after starting that dosage you experienced it
  • the specific symptoms of the side effect
  • how it affected your daily activities
  • any other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how the drug affects you. And your doctor can use this information to adjust your treatment plan if needed.

Femara 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 Femara. The list below includes factors to consider.

Liver problems. Before you take Femara, tell your doctor if you have any liver problems, including cirrhosis. Severe liver problems can cause the level of Femara to build up in your body, which can raise your risk for side effects. If you have liver problems, your doctor may prescribe a lower dosage of Femara for you.

Allergic reaction. If you’ve had an allergic reaction to Femara or any of its ingredients, you shouldn’t take Femara. Ask your doctor what other medications are better options for you.

Osteoporosis. Femara can weaken your bones, which may cause new or worsened osteoporosis. If you have osteoporosis or risk factors* for developing this condition, talk with your doctor before starting Femara. They may want to prescribe medication to help protect your bones during your Femara treatment.

* Risk factors for osteoporosis include a family history of the condition, low physical activity, smoking, drinking alcohol, and a diet low in calcium and vitamin D.

Alcohol use and Femara

It should be safe to drink alcohol during your Femara treatment.

However, it’s important to note that alcohol and Femara can have similar side effects. If you do drink alcohol while taking Femara, you might be more likely to experience:

If you plan to drink alcohol while taking Femara, talk with your doctor about how much may be safe for you to drink.

Pregnancy and breastfeeding while taking Femara

Femara should not be used during pregnancy or while breastfeeding. You should not become pregnant or breastfeed for at least 3 weeks after your last dose of Femara.

Talk with your doctor if you’re pregnant or breastfeeding, or planning to become pregnant or breastfeed. Your doctor can recommend other treatments, besides Femara, that are safe for you to use.

Femara can be an effective treatment option for certain types of breast cancer. But some people may experience side effects while taking this drug.

When talking with your doctor, you may want to ask the following questions:

  • What could happen if I become pregnant during my Femara treatment?
  • How do Femara’s side effects compare with those of other cancer drugs?
  • Do I have a higher risk for side effects than other people taking Femara?

To learn more about breast cancer and its treatment options, sign up for Healthline’s breast cancer newsletter.

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.