Arimidex

Introduction

Written by Kirstyn Hill, PharmD, MPH
Medically reviewed by Alex Brewer, PharmD, MBA
Updated on September 8, 2023

Anastrozole (an AS troe zole) is a generic medication prescribed for treatment of certain types of breast cancer. Anastrozole belongs to a group of drugs called aromatase inhibitors.

Side effects of anastrozole

Anastrozole may cause mild or serious side effects. More common mild side effects of anastrozole and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about anastrozole’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for anastrozole listed in the “Resources” section.

Mild side effects

More common mild side effects reported with anastrozole are listed below.

This article doesn’t include all possible mild side effects of the drug. To learn more about anastrozole’s side effects, refer to the prescribing information for anastrozole listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Anastrozole oral tablet’s mild side effects include:

• hot flashes
• decreased energy
• joint pain
• high blood pressure
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for anastrozole” section.

Serious side effects

Serious side effects of anastrozole are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about anastrozole’s side effects, refer to the prescribing information for anastrozole listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, anastrozole’s serious side effects include:

• skin reactions, such as sores and blisters
• high cholesterol levels
• decreased bone mineral density, which may increase the risk of fractured bones
• liver problems, such as jaundice, liver pain, and cirrhosis*
• severe allergic reaction†

* This side effect wasn’t reported in studies of anastrozole. But it has occurred in people after the drug was approved for use.
† For details about this side effect, see the “Interactions and warnings for anastrozole” section.

Common questions about anastrozole

Below, you’ll find answers to a few commonly asked questions about anastrozole.

Can men take anastrozole for breast cancer?

Not usually. Anastrozole is approved by the Food and Drug Administration (FDA) to treat certain types of breast cancer in females* who have gone through menopause. The FDA has not approved the use of anastrozole for breast cancer in males.* (For information on the types of breast cancer anastrozole is used to treat, see the “Uses of anastrozole” section.)

However, anastrozole may be prescribed off-label to treat hormone receptor-positive breast cancer in males. With off-label use, doctors prescribe a drug for a purpose other than what it’s approved for.

If you’d like information on the off-label use of anastrozole or breast cancer treatments for males, talk with your doctor or pharmacist.

* Sex and gender exist on spectrums. In this article, we use the terms “men,” “males,” and “females” to refer to sex assigned at birth.

Are there certain foods to avoid while taking anastrozole?

No, there are no foods that you need to avoid while taking anastrozole. Some foods may interact with certain medications, but this is not the case with anastrozole. You may take this drug with or without food.

Based on how anastrozole works, there was some concern that soy products may interact with anastrozole. (Examples of soy products are tofu and soy milk.) But studies have not shown that soy affects how well anastrozole works.

For information about anastrozole interactions, see the “Interactions and warnings for anastrozole” section. You can also talk with your doctor or pharmacist about possible interactions with this drug.

How does anastrozole work? And how long does it take to start working?

Anastrozole works by decreasing the amount of estrogen in your body. This drug is typically prescribed to treat hormone receptor-positive (HR-positive) breast cancer. With this type of breast cancer, hormones such as estrogen help the cancer cells to grow.

In females who have gone through menopause, estrogen is mainly created by the enzyme aromatase. (Enzymes are proteins that help with chemical changes in the body.) Anastrozole blocks aromatase from making estrogen in the body. This helps to decrease the size of a breast cancer tumor or delay worsening of the cancer.

Anastrozole will immediately start to decrease the amount of estrogen in your body. However, it takes several weeks to months for the drug to reach its full effect.

If you’d like to know more about how anastrozole works, talk with your doctor or pharmacist.

Uses of anastrozole

The Food and Drug Administration (FDA) approves prescription drugs such as anastrozole for certain conditions. Approved uses for anastrozole are described below.

Use for breast cancer

Doctors may prescribe anastrozole tablet for treating certain types of breast cancer. It’s used for this purpose in females* who have gone through menopause. It’s usually prescribed as a long-term treatment.

Specifically, anastrozole is used to treat:

• Early breast cancer that is hormone receptor-positive (HR-positive). For this purpose, anastrozole is prescribed for use after surgery to remove the cancer. It’s taken to help lower the risk of the cancer returning.
• Locally advanced or metastatic breast cancer that is HR-positive or has an unknown hormone receptor status. For this use, anastrozole is prescribed as a first-line treatment (preferred first treatment option for a disease).
• Advanced breast cancer that has progressed after tamoxifen therapy. (Like anastrozole, tamoxifen works by blocking estrogen. However, the way these drugs block estrogen differs.)

Breast cancer causes breast cells to grow uncontrollably. These cells can group together to form a tumor. With early breast cancer, a small tumor develops in the breast or nearby lymph nodes, which are part of your immune system. Locally advanced breast cancer involves larger tumors in the breast or lymph nodes. The cancer may also have spread to nearby areas outside the breast, such as the skin, ribs, or muscles. With metastatic breast cancer, the cancer has spread to areas farther away from the breast.

HR-positive breast cancer is cancer that responds to hormones such as estrogen. When present, such hormones promote the growth of this type of cancer.

Signs and symptoms of breast cancer include:

• a lump in the breast
• swelling of the breast
• nipple discharge
• breast or nipple pain
• inverted nipple

* Sex and gender exist on spectrums. In this article, we use the term “female” to refer to a person’s sex assigned at birth.

Interactions and warnings for anastrozole

Below, you’ll find information about anastrozole’s possible interactions and warnings.

Interactions of anastrozole

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take anastrozole, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for anastrozole” section below.

Warnings for anastrozole

Some people should not take anastrozole, and others should take it cautiously.

Anastrozole could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether anastrozole is a safe option for you.

Ask your doctor about specific warnings for anastrozole, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Anastrozole can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to anastrozole or any of its ingredients, your doctor will likely not prescribe anastrozole. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

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

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to anastrozole, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of anastrozole

If you take anastrozole, you should not take more anastrozole than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much anastrozole, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and anastrozole

Information about anastrozole and pregnancy and breastfeeding is described below.

Anastrozole and pregnancy

It’s not known whether anastrozole should be taken during pregnancy. The drug is only approved for use in females* who have gone through menopause. Studies of anastrozole didn’t include people who can become pregnant.

If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication. Your doctor may suggest birth control options to use during treatment with anastrozole.

* Sex and gender exist on spectrums. In this article, we use the term “female” to refer to a person’s sex assigned at birth.

Anastrozole and breastfeeding

Anastrozole should not be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication. Your doctor may recommend other ways to feed your child during treatment with anastrozole.

What to ask your doctor

Let your doctor know if you have questions about anastrozole or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Is anastrozole a type of chemotherapy?
• Can my breast cancer come back after I finish anastrozole treatment?
• What happens if I miss a dose of anastrozole?

Resources

• Anastrozole tablets for oral use. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/f86d2158-b078-3f74-e053-6394a90aa4b6/spl-doc
• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Magee PJ, et al. (2012). Soy products in the management of breast cancer. https://journals.lww.com/co-clinicalnutrition/abstract/2012/11000/soy_products_in_the_management_of_breast_cancer.11.aspx

Disclaimer: Optum Perks 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.