Arimidex (Anastrozole) - Oral

What Is Arimidex?

Arimidex (anastrozole) is a prescription medication used to treat hormone receptor-positive (HR+) breast cancer. It is an antineoplastic drug, part of the aromatase inhibitor medication class. Antineoplastic drugs are used to treat cancer, with aromatase inhibitors specifically targeting certain types of breast cancer.

The term “HR+” is used when the breast cancer cells have either estrogen or progesterone receptors or both. Arimidex works to reduce estrogen in the body by preventing other hormones from turning into estrogen, slowing the growth of these breast cancer tumors. It is available in tablet form for oral use.

Drug Facts

Generic Name: Anastrozole

Brand Name(s): Arimidex

Drug Availability: Prescription

Therapeutic Classification: Antineoplastic agent

Available Generically: Yes

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Anastrozole

Dosage Form(s): Tablet

What Is Arimidex Used For?

Arimidex is often used to treat HR+ breast cancer following other treatments for breast cancer–such as chemotherapy, surgery, or radiation–or in breast cancer that has spread to other parts of the body (metastatic).

The Food and Drug Administration (FDA) approved Arimidex for use in postmenopausal people as:

  • Add-on (adjuvant) treatment of HR+ early breast cancer
  • Initial treatment of HR+ or hormone receptor unknown breast cancer that has spread to other parts of the body
  • Treatment of advanced breast cancer that no longer responds to tamoxifen therapy

Verywell / Dennis Madamba

How to Take Arimidex

Take this medication as directed by your healthcare provider. Arimidex can be taken with or without food and should be taken once a day, around the same time each day.


Keep Arimidex at room temperature (between 68 F and 77 F) and away from moisture or heat. It is safe to travel with this medication.

Off-Label Uses

Healthcare providers can prescribe Arimidex off-label for other reasons. Off-label use refers to when an FDA-approved drug is used for other conditions that it is not indicated to treat.

Arimidex may be used off-label for the following conditions:

What Are the Side Effects of Arimidex?

This is not a complete list of side effects, and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at or 1-800-FDA-1088.

As with all drugs, Arimidex may cause side effects. Although uncommon, some side effects from Arimidex may be severe. Be sure to mention any side effects you experience to your healthcare provider.

Common Side Effects

Some commonly associated side effects with taking Arimidex can include:

  • Hot flashes
  • Fatigue
  • Joint pain
  • Elevated blood pressure
  • Osteoporosis (bone disease)
  • Headache
  • Difficulty sleeping
  • Cough
  • Shortness of breath
  • Elevated cholesterol levels

Severe Side Effects

Severe side effects can include:

  • Allergic reaction that results in swelling of the lips, tongue, or throat
  • Skin reactions, which can cause blistering or ulcers
  • Liver dysfunction, which can cause elevated liver enzymes, abdominal pain, liver swelling, or yellowing of the skin or eyes
  • Worsening heart disease in women with pre-existing heart disease due to decreased blood flow in the blood vessels of the heart

If you’re experiencing any serious side effects, be sure to contact your healthcare provider immediately. If the symptoms are life-threatening or if you’re having a medical emergency, call 911 or go to your nearest emergency room.

Long-Term Side Effects

Arimidex has the potential to decrease bone density with long-term use, leading to an increase in the possibility of bone fractures.

Report Side Effects

Arimidex may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Arimidex Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (tablets):
    • For breast cancer:
      • Adults—1 milligram (mg) once a day.
      • Children—Use and dose must be determined by your doctor.


There are no modifications required for Arimidex.

Missed Dose

If you miss a dose of Arimidex, take it as soon as you remember on the same day. If it is close to the time for the second dose, the dose should be skipped.

Overdose: What Happens If I Take Too Much Arimidex?

There has not been an established overdose of Arimidex. In some studies, very high doses of Arimidex were taken without any adverse side effects. However, if you do take too much Arimidex, contact your prescriber for further instructions.

What Happens If I Overdose on Arimidex?

If you think you or someone else may have overdosed on Arimidex (anastrozole), call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking anastrozole, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly. Blood tests may be needed to check for unwanted effects.

It is unlikely that a postmenopausal woman may become pregnant. But, you should know that using this medicine while you are pregnant could harm your unborn baby. Use an effective form of birth control during treatment with this medicine and for at least 3 weeks after the last dose. If you think you have become pregnant while using this medicine, tell your doctor right away.

Do not use this medicine together with tamoxifen (Nolvadex®, Soltamox®).

This medicine may cause serious allergic reactions, including anaphylaxis and angioedema, which can be life-threatening and require immediate medical attention. Call your doctor right away if you have itching, hives, hoarseness, trouble breathing or swallowing, or any swelling of your hands, face, or mouth while you are using this medicine.

Check with your doctor right away if you start having chest pains or difficulty with breathing. This medicine may increase the chance of heart problems, including heart attack, in women who have a history of ischemic heart disease.

This medicine may decrease bone mineral density when used for a long time. A low bone mineral density can cause weak bones or osteoporosis. If you have any questions about this, talk to your doctor.

This medicine may increase your cholesterol or fat in the blood. If this happens, your doctor may give you medicine to lower the cholesterol and fat.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines for appetite control, asthma, colds, cough, hay fever, or sinus problems, and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Arimidex?

People who are pregnant or breastfeeding should not take Arimidex.

What Other Medications Interact With Arimidex?

A few medications should be avoided when taking Arimidex. These medications include:

  • Tamoxifen
  • Estrogen or estrogen-containing medications

What Medications Are Similar?

There are two other medications in the class of aromatase inhibitors: Femara (letrozole) and Aromasin (exemestane). Both of these medications also work by blocking other hormones from being turned into estrogen. These should not be taken along with Arimidex.

Frequently Asked Questions

  • What is Arimidex used for?

    Arimidex is an oral medication used to treat hormone receptor-positive breast cancer in people who have gone through menopause. It can be taken after surgery, chemotherapy, and/or radiation. It may also be used for breast cancer that is metastatic, meaning it has spread to other areas of the body.

  • How does Arimidex work?

    After menopause, the body continues to produce estrogen by changing another hormone type, called androgens, into estrogen. Arimidex blocks this process from happening, thereby reducing the amount of estrogen in the body. Estrogen promotes the growth of certain breast cancers.

  • What are the side effects of Arimidex?

    Side effects that may be experienced by someone who takes Arimidex can include:

    • Fatigue
    • Hot flashes
    • Bone pain
    • Joint pain
    • Osteoporosis
    • Headache
    • Difficulty sleeping

How Can I Stay Healthy While Taking Arimidex?

Staying on Arimidex for the prescribed length of time is an important part of breast cancer treatment. If you’re experiencing any side effects from Arimidex that make you want to stop taking it, please talk with your healthcare team. They may be able to help you manage these side effects or have other suggestions to help you feel better.

Medical Disclaimer

Verywell Health's drug information is meant for education purposes only and not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your doctor before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. US National Library of Medicine. DailyMed - ARIMIDEX- anastrozole tablet.

  2. DiGiorgio L, Sadeghi-Nejad H. Off label therapies for testosterone replacement. Transl Androl Urol. 2016;5(6):844-849. doi:10.21037/tau.2016.08.15

  3. American Cancer Society. Hormone therapy for breast cancer.

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.