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Aromatase Inhibitors for Breast Cancer

Table of Contents

Aromatase Inhibitors for Breast Cancer


Generic NameBrand Name

Aromatase inhibitors are available as tablets. Follow your doctor's orders or the directions on the label.

How It Works

Aromatase inhibitors interfere with how much estrogen the body's tissues can make. This limits the amount of estrogen available in the body.

An aromatase inhibitor cannot lower estrogen levels made by the ovaries. That is why an aromatase inhibitor only works after menopause, when a woman's ovaries have stopped making estrogen and other hormones.

Why It Is Used

Aromatase inhibitors are used to treat early estrogen receptor-positive (ER+) breast cancer. They are also used to treat metastatic or recurrent ER+ breast cancer. An aromatase inhibitor can be used alone or after tamoxifen treatment.

Some doctors may use aromatase inhibitors "off-label" to treat infertility and endometriosis. This means that the U.S. Food and Drug Administration (FDA) has not approved this use.

How Well It Works

Aromatase inhibitors make it less likely that breast cancer will come back. These medicines work well for postmenopausal women who have had ER+ breast cancer. Studies that compare survival rates for aromatase inhibitors and tamoxifen show that women live about the same length of time when taking either of these medicines.1

Aromatase inhibitors may be given to postmenopausal women who have breast cancer, either at the beginning of treatment or after they are given tamoxifen.

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

Call 911 or other emergency services right away if you have:

Call your doctor if you have:

Common side effects of this medicine include:

Letrozole and anastrozole can increase your cholesterol.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

Do not use this medicine if you are pregnant or planning to get pregnant. If you need to use this medicine, talk to your doctor about how you can prevent pregnancy.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF) to help you understand this medication.



  1. National Cancer Institute (2013). Breast Cancer Treatment (PDQ)—Health Professional Version. Available online:

Credits for Aromatase Inhibitors for Breast Cancer

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer Douglas A. Stewart, MD - Medical Oncology
Last Revised August 14, 2013

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