Arimidex (anastrozole) is a prescription drug that’s used to treat breast cancer. Arimidex can cause side effects that range from mild to serious. Side effects may include hair loss, hot flashes, and pain.

Arimidex is used to treat certain types of breast cancer in females* who’ve gone through menopause (stopped having periods). Specifically, it’s prescribed in some cases to treat the following:

The active ingredient in Arimidex is anastrozole. (An active ingredient is what makes a drug work.)

Arimidex is a tablet that is taken by mouth. It comes in a strength of 1 milligram (mg).

Keep reading to learn about the common, mild, and serious side effects that Arimidex can cause. For more information about Arimidex, including details about its uses, see this in-depth article.

* 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.

Below are just a few of the more common side effects reported by people who took Arimidex in studies. These side effects can vary depending on what condition the drug is being used to treat.

More common side effects in people taking Arimidex for early breast cancer include:

More common side effects in people taking Arimidex for advanced or metastatic breast cancer include:

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

These are just a few of the side effects Arimidex may cause. Read on to learn about other possible mild and serious side effects of the drug.

Examples of mild side effects that have been reported with Arimidex for early breast cancer treatment include:

Examples of mild side effects that have been reported with Arimidex for advanced or metastatic breast cancer treatment include:

  • hot flashes
  • nausea
  • headache*
  • weakness
  • sore throat
  • back pain
  • bone pain*
  • cough
  • swelling of the arms or legs
  • hair loss*

* To learn more about this side effect, see the “Side effects explained” section 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 using Arimidex unless your doctor recommends it.

Arimidex may cause mild side effects other than the ones listed above. See the Arimidex 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 Arimidex, visit MedWatch.

Serious side effects that have been reported with Arimidex include:

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

If you develop serious side effects while taking Arimidex, 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.

Get answers to some frequently asked questions about Arimidex’s side effects.

What side effects of Arimidex are possible after 5 years of treatment?

Arimidex may be used as a long-term treatment option for breast cancer. Studies looked at side effects that occurred in females* for 5 years after starting Arimidex treatment. In some cases, the studies continued to monitor side effects in females for 5 years after stopping treatment (10 years total).

Any of the mild or serious side effects listed in the sections above may occur after 5 years of treatment with Arimidex. For more about long-term side effects that may last even after stopping Arimidex treatment, see “Can Arimidex cause long-term side effects that result in permanent damage?” below.

If you have additional questions about possible side effects that can occur after 5 years of treatment, talk with your doctor or pharmacist.

* 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.

Do Arimidex side effects differ for men and women?

At this time, Arimidex is only used in females.* The medication isn’t approved for use in males* with breast cancer or other conditions. Since this drug hasn’t been studied in males, possible side effects of Arimidex in males are unknown.

Arimidex works by decreasing levels of estrogen, which is a female hormone. This medication may be used by males to decrease their estrogen levels if they’re taking other drugs that increase estrogen. (An example is anabolic steroids.) Athletes or bodybuilders may use Arimidex for this purpose. But this use of Arimidex is illegal, and the drug may be tested for prior to sporting events or competitions.

If you’re male and your doctor has recommended that you take Arimidex, talk with them about the drug’s possible side effects.

* Sex and gender exist on spectrums. Use of the terms “male” and “female” in this article refers to sex assigned at birth.

Can Arimidex cause long-term side effects that result in permanent damage?

Yes, Arimidex may cause some long-term side effects. In some rare cases, side effects can result in permanent damage, even after you stop treatment with Arimidex.

Examples of the long-term side effects of Arimidex include:

It’s possible to develop these side effects from taking Arimidex for a long time or at any time during treatment. Some side effects may last even after you stop treatment, such as osteoporosis or high cholesterol.

If you have questions about the long-term effects of Arimidex, ask your doctor.

Does Arimidex cause cardiotoxicity or liver toxicity?

Although rare, it’s possible for Arimidex to cause cardiotoxicity or liver toxicity. Cardiotoxicity is damage that can occur to the heart that may affect how well it works. Similarly, liver toxicity is damage to the liver that may affect its function.

If you have any liver or heart conditions, tell your doctor before starting Arimidex. They may monitor you more often throughout your treatment, or they may recommend a different medication for you.

If you develop symptoms of heart problems at any time during treatment, seek medical attention right away. Examples include chest pain or shortness of breath. Similarly, seek medical attention right away if you develop symptoms of a liver condition, such as yellowing of the eyes or skin. Your doctor will try to find out the cause of your symptoms.

Learn more about some of the side effects Arimidex may cause.

Hair loss

Although rare, it’s possible to develop hair loss while taking Arimidex. This side effect was only reported in people taking the drug for advanced breast cancer.

What might help

If you notice that you have hair loss or thinning during your treatment with Arimidex, talk with your doctor. They may be able to recommend a medication or other ways to prevent more hair loss from occurring.

Headache

You may have headaches from taking Arimidex. Headaches were one of the most common side effects that people taking this medication reported.

What might help

If you have headaches from taking Arimidex, talk with your doctor about the best way to treat them. They may be able to recommend an over-the-counter (OTC) pain reliever, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), to help ease your headache.

Bone pain

Arimidex can cause bone pain. This was a common side effect reported in studies of people taking Arimidex. Bone pain can occur in anyone taking Arimidex. But this side effect was more commonly reported in those taking the medication for advanced breast cancer.

What might help

If you develop bone pain, talk with your doctor. They may be able to recommend ways to reduce the pain. For example, they may recommend taking an OTC pain reliever, such as acetaminophen or ibuprofen, to help ease this side effect.

Liver problems

Although not common, it’s possible to have liver problems from taking Arimidex. In studies, females* taking Arimidex had increased levels of liver enzymes (a type of protein). Higher levels of liver enzymes may indicate liver damage.

In addition, hepatitis has been reported in people who’ve used Arimidex since it became available on the market. (Hepatitis is inflammation of the liver.) But it’s important to note that this side effect wasn’t seen in studies of Arimidex. And it’s unclear how often it occurred or whether Arimidex was the cause.

If you have symptoms of a liver problem, you should contact your doctor right away. Symptoms to watch for include:

* 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.

What might help

Your doctor may monitor your liver function throughout Arimidex treatment to check for liver problems. If you develop symptoms of a liver condition, contact your doctor right away. They may recommend that you try a different medication.

Allergic reaction

Like most drugs, Arimidex can cause an allergic reaction in some people.

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. To manage your symptoms, they may suggest an over-the-counter antihistamine you take by mouth, such as diphenhydramine (Benadryl). Or they may recommend a product you apply to skin, such as hydrocortisone cream.

If your doctor confirms you had a mild allergic reaction to Arimidex, they’ll decide if you should continue using 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 you had a serious allergic reaction to Arimidex, they may have you switch to a different treatment.

Keeping track of side effects

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

Your side effect notes can include things such as:

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

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

Arimidex 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 Arimidex. The list below includes factors to consider.

Osteoporosis. Arimidex may weaken your bones and increase your risk of bone fractures. If you have osteoporosis, you may already have weak bones or bones that are more likely to fracture. In this case, taking Arimidex may further increase your risk of bone fractures. Your doctor may monitor your bone mineral density or may recommend a different treatment option for you.

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

High cholesterol. Arimidex may increase your cholesterol. If you already have high cholesterol, taking Arimidex may make your cholesterol levels even worse. Your doctor will likely monitor your cholesterol levels throughout your treatment with Arimidex. If your levels become too high, they may recommend that you take another medication to lower your cholesterol.

Coronary artery disease. If you have coronary artery disease, also known as ischemic heart disease, tell your doctor before starting Arimidex. If you have this condition, taking Arimidex can increase your risk of a heart or blood vessel problem, such as a heart attack. Your doctor may recommend a different treatment option for you.

Liver problems. Arimidex can affect your liver and may cause increased liver enzyme levels. In some cases, this may be a sign of liver damage. If you have a liver condition, taking Arimidex may increase your risk of liver problems or worsening of your liver condition. Your doctor may monitor your liver more often throughout treatment, or they may recommend a different medication for you. For more information, see “Liver problems” in the “Side effects explained” section above.

Females* who have not gone through menopause. Arimidex is only approved to be used in females who’ve gone through menopause (stopped having periods). This medication has not been studied for use in females who haven’t gone through menopause. If you haven’t gone through menopause, talk with your doctor about the best treatment option 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.

Alcohol and Arimidex

There are no known interactions between alcohol and Arimidex.

But some of the side effects caused by Arimidex may also be caused by drinking alcohol. For example, both can cause headaches, nausea, and vomiting. So drinking alcohol while taking Arimidex may increase your risk of these side effects.

In addition, Arimidex may affect your liver. Because alcohol can also affect your liver, drinking alcohol and taking Arimidex may further increase your risk of liver problems.

If you’re taking Arimidex, talk with your doctor about how much alcohol, if any, is safe for you to drink.

Pregnancy and breastfeeding while taking Arimidex

It’s not known if Arimidex is safe to take during pregnancy. But due to the way that Arimidex works, it may cause harm to a developing fetus. If you can become pregnant, you should use birth control while taking Arimidex. You should also continue to use birth control for at least 3 weeks after you stop taking the drug.

It’s not known if Arimidex is safe to take while breastfeeding, or if the drug may be present in breast milk. But it’s not recommended that you breastfeed while taking Arimidex or for at least 2 weeks after stopping treatment.

If you’re pregnant or breastfeeding, or planning to become pregnant or breastfeed, talk with your doctor before starting Arimidex.

In most cases, side effects that you experience from taking Arimidex will be mild. But it’s also possible to develop serious side effects from this medication.

It’s a good idea to know the side effects that may occur with Arimidex so that you can monitor for them. Before you start taking Arimidex, talk with your doctor about its side effects. Here are some questions you may wish to ask:

  • Am I at an increased risk of side effects due to my other medical conditions?
  • How should I treat side effects that I have from Arimidex?
  • What should I do if I become pregnant while taking Arimidex?

To learn more about Arimidex, see these articles:

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Q:

Does taking Arimidex with other treatments for cancer increase the risk of side effects?

Anonymous

A:

Arimidex can safely be used with other treatments for your breast cancer. For example, your doctor may suggest using Arimidex with fulvestrant (Faslodex) or with abemaciclib (Verzenio) based on the type of treatment they recommend.

But it’s possible that Arimidex, when used with other treatments for cancer, may increase the side effects you have.

Studies didn’t look at the occurrence of side effects when Arimidex was used with other medications to treat breast cancer. If you’re concerned about medications that may interact with Arimidex, talk with your doctor or pharmacist.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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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.