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Trade/other name(s): Arimidex

Why would this drug be used?

Anastrozole is used to treat certain kinds of breast cancer in women who are past menopause. It is also being studied for other uses.

How does this drug work?

Anastrozole belongs to a group of drugs called aromatase inhibitors. Normally in the body, some of the androgens (male hormones) that are made by the adrenal glands are converted to estrogen by an enzyme in fat tissue called aromatase. This drug blocks aromatase so that estrogen isn’t formed that way. This lowers estrogen levels in women who do not have functioning ovaries. This drug doesn’t affect estrogen production from the ovaries, so has little effect on estrogen levels in women whose ovaries are working. If estrogen levels are lowered, breast cancers that need estrogen to grow may stop growing or decrease in size.

Before taking this medicine

Tell your doctor…

  • If you are allergic to anything, including medicines, dyes, additives, or foods.
  • If you have any serious medical conditions, such as high cholesterol, heart disease, or liver disease (including cirrhosis)
  • If you are pregnant, trying to get pregnant, or if there is any chance of pregnancy. This drug may cause birth defects if it is taken during pregnancy. Check with your doctor about what kinds of birth control can be used with this medicine.
  • If you are breast-feeding. It is not known whether this drug passes into breast milk. If it does, it could harm the baby.
  • If you are still having menstrual periods. This drug is only for women who do not have functioning ovaries, such as those who are past menopause.
  • About any other prescription or over-the-counter medicines you are taking, including vitamins and herbs. In fact, keeping a written list of each of these medicines (including the doses of each and when you take them) with you in case of emergency may help prevent complications if you get sick.

Interactions with other drugs

Medicines that contain estrogen (hormone therapies, birth control pills or patches) raise estrogen levels and counter the action of anastrozole.

Check with your doctor, nurse, or pharmacist about other medicines, vitamins, herbs, and supplements, and whether alcohol can cause problems with this medicine.

Interactions with foods

No serious interactions with food are known at this time. Check with your doctor, nurse, or pharmacist about whether foods may be a problem.

Tell all the doctors, dentists, nurses, and pharmacists you visit that you are taking this drug.

How is this drug taken or given?

Anastrozole is a pill and should be taken once a day, about the same time each day. It can be taken with or without food. The dose is the same for all adults. Take this drug exactly as your doctor tells you to. If you do not understand the instructions, your doctor or nurse can explain them to you.

Store the medicine in a tightly closed container and away from children and pets.


It is important to keep taking this drug, even if you feel well. If you are bothered by side effects, talk to your doctor or nurse to find out if the problems are serious. Many side effects can be managed with help from your doctor.

Because this drug lowers estrogen levels, it can weaken bones and lead to a condition called osteoporosis. Bones that become weak can break (fracture) more easily.

This drug may increase the risk of heart attacks in women who already have blockages in the blood vessels to the heart. Get emergency help for any symptoms of a heart attack, such as pain or pressure in the chest or shortness of breath.

This drug may increase cholesterol levels, so your doctor may watch these levels while you are on treatment.

Rarely, this drug can affect the liver. Call your doctor right away if you notice any yellowing of the skin or eyes, pain in the upper right part of the stomach, or any darkening of the urine.

Very rarely, this drug may cause blood clots. This can take the form of clots in arms or legs (deep vein thrombosis), stroke, or a blockage in the lungs. Call your doctor or nurse right away if you notice pain in your lower leg (calf), redness or swelling of your arm or leg. Get emergency help if you have shortness of breath, chest pain, or trouble speaking or moving.

This drug should not be taken during pregnancy because it can harm the fetus.

This drug is only helpful in women who do not have functioning ovaries (such as those who are past menopause). If you had your uterus removed (a hysterectomy) but still have your ovaries, blood tests of hormone levels may need to be done to see if your ovaries have stopped working (and you have truly gone through menopause).

Possible side effects

You will probably not have most of the following side effects, but if you have any talk to your doctor or nurse. They can help you understand the side effects and cope with them.


  • Hot flashes
  • Bone or joint pain

Less common

  • Weakness
  • Lower energy level
  • Headache
  • Nausea and vomiting
  • Mild diarrhea
  • Increased or decreased appetite
  • Sweating
  • Vaginal dryness
  • Bone weakness or thinning, including osteoporosis
  • Broken bones (fracture)
  • Thinning hair
  • Mood disturbances (depression or anxiety)
  • Trouble sleeping
  • Numbness, tingling, or tickling in hands or feet
  • Swelling of the legs, ankles, feet, arms, or hands
  • Increase in cholesterol levels


  • Vaginal bleeding
  • Blood clots in veins of the arm or leg (deep venous thrombosis), the arteries of the lung (pulmonary embolus), or to the brain (stroke)
  • Heart attacks or angina*
  • Abnormal blood test results suggesting the drug may be affecting the liver (Your doctor will discuss the importance of this finding, if any.)*
  • Allergic reaction with itchy welts, swelling of the face, lips, tongue or throat, which can cause trouble swallowing or breathing
  • Death due to heart attack, stroke, pulmonary embolus (blood clot in the lung), or some other cause

*See “Precautions” section for more detailed information.

There are other side effects not listed above that can also occur in some patients. Tell your doctor or nurse if you develop these or any other problems.

FDA approval

Yes – first approved in 1995

Disclaimer: This information does not cover all possible uses, actions, precautions, side effects, or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for talking with your doctor, who is familiar with your medical needs.

Last Medical Review: 08/07/2014
Last Revised: 08/07/2014