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Aromatase Inhibitors for Breast Cancer


Generic NameBrand Name
anastrozoleArimidex, Aromasin, Femara
exemestaneArimidex, Aromasin, Femara
letrozoleArimidex, Aromasin, Femara

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.1

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.2

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

Side effects of an aromatase inhibitor may include:

  • Hot flashes.
  • Muscle or body aches.
  • Mild nausea.
  • Diarrhea or constipation.
  • A general feeling of illness.
  • Weakness and fatigue.
  • Bone thinning. Aromatase inhibitors increase the rate of bone thinning that occurs normally in postmenopausal women.

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

What To Think About

For breast cancer treatment, aromatase inhibitors should be given only under the supervision of a medical oncologist.

Complete the new medication information form (PDF)Click here to view a form.(What is a PDF document?) to help you understand this medication.



  1. Smith IE, Chua S (2006). ABC of breast diseases. Medical treatment of early breast cancer. I: Adjuvant treatment. BMJ, 332(7532): 34–37.

  2. National Cancer Institute (2011). Breast Cancer PDQ: Treatment – Health Professional Version. Available online:


ByHealthwise Staff
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerDouglas A. Stewart, MD - Medical Oncology
Last RevisedAugust 11, 2011

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