Anastrozole (Arimidex): What to Expect, Side Effects, and More
Anastrozole (brand name: Arimidex) is a hormonal therapy medicine used to treat post-menopausal women.
If you’ve been diagnosed with breast cancer and have been through menopause, either naturally or surgically — or if your doctor has also prescribed medication to put you in menopause temporarily — you may be prescribed anastrozole
to reduce the risk of hormone receptor-positive, early-stage breast cancer coming back (recurring) after surgery
as a first treatment for hormone receptor-positive, advanced-stage breast cancer
as a treatment for advanced-stage breast cancer that grew during treatment with tamoxifen
to reduce the risk of developing breast cancer in postmenopausal women who are at high risk
Anastrozole should not be taken at the same time as tamoxifen because together, they may be less effective and can cause additional side effects.
See anastrozole (Arimidex) prescribing information.
How anastrozole works
Anastrozole is an aromatase inhibitor — it works by blocking the enzyme aromatase, which turns the hormone androgen into small amounts of estrogen in the body. This means less estrogen is available to stimulate the growth of hormone receptor-positive breast cancer cells.
Other aromatase inhibitors include letrozole (Femara), and exemestane (Aromasin).
What to expect during anastrozole treatment
Anastrozole is a pill taken once per day. The typical dosage is 1 mg.
If you’ve been diagnosed with early-stage, hormone receptor-positive breast cancer, you’ll likely be advised to take anastrozole for at least five years after surgery to reduce the risk of recurrence.
After five years, if breast cancer had been found in the lymph nodes, called node-positive disease, a woman may be advised to take anastrozole or another aromatase inhibitor for an additional five years, for a total of 10 years of hormonal therapy treatment.
If you’ve been diagnosed with advanced-stage, hormone receptor-positive breast cancer, you’ll continue to take anastrozole as long as the benefits of the medicine outweigh any side effects.
Anastrozole side effects
Like almost all breast cancer medicines, anastrozole can cause side effects, some of them severe.
The most common side effects of anastrozole are:
broken bones
More rarely, anastrozole also may cause serious side effects, including:
Heart problems: Anastrozole may increase the risk of heart problems in people with narrowed heart arteries (also called ischemic heart disease or coronary heart disease). If you have heart disease, you and your doctor will weigh the risks and benefits of anastrozole for you.
Bone loss: Because anastrozole lowers the amount of estrogen in the body, less estrogen reaches bone cells, which can lead to bone thinning and weakening and a higher-than-average risk of breaking a bone. If you’ve been diagnosed with osteopenia or osteoporosis, your doctor may recommend that you take a different hormonal therapy medicine, such as tamoxifen, rather than anastrozole, or may prescribe other medications to increase your bone strength or prevent further bone loss. Your doctor also will likely monitor your bone density while you’re taking anastrozole.
High cholesterol: In some cases, anastrozole can increase your blood cholesterol levels. If you have high cholesterol, your doctor will likely monitor your cholesterol levels while you’re taking anastrozole.
Because many women diagnosed with breast cancer have low vitamin D levels, your doctor will likely monitor your levels while you’re taking anastrozole. If you have a vitamin D deficiency, your doctor may also recommend a supplement.
You shouldn’t take anastrozole if you’re pregnant, trying to get pregnant, or breastfeeding. The medicine may cause damage to developing embryos and pregnancy loss. You should use an effective non-hormonal birth control while you are taking anastrozole. You should use birth control for at least three weeks after your last dose of anastrozole.
What happens when you stop taking anastrozole?
If you’re on anastrozole to treat breast cancer, stopping before your doctor recommends may increase your risk of recurrence. Research shows that if you take it for 10 years, your risk of recurrence decreases in some cases.
If you’re at a high risk of developing breast cancer and take anastrozole for five years, it continues to reduce your risk even after you stop. The International Breast Cancer Intervention Study II (IBIS-II) Prevention trial showed that this protection lasted at least 11 years after stopping the medication.
Some side effects — such as nausea, hot flashes, pain, and weakness, should resolve within a few weeks of stopping anastrozole. Other side effects, like high cholesterol, lymphedema, and osteoporosis may take longer to subside or may continue indefinitely.
If you’re considering stopping hormonal therapy because of side effects, talk to your doctor right away. There are steps you can take to ease some of the most common side effects.
Real patient reviews
Members of our community discuss their experiences with anastrozole in the community forum. Here are some of their comments. Remember, it's essential to talk to your doctor about any side effects you're having and ask about ways to manage them.
“I've been on anastrozole since February of this year (only 4 more years to go!!). I have hot flashes and night sweats, but nothing unbearable. What has suddenly gotten worse is the joint pain in my feet and thumbs. It's only bad when I first get up in the morning, but after I get up and moving, it gets better. Luckily, it hasn't stopped me from working out. I didn't have any of the weight gain that other people have talked about; actually, I have lost 10 pounds since I started the medicine.” —dngdonnelly
“I've had no side effects that I'm aware of from the anastrozle. I'm thankful for that.” —sunshine99
“I never did experience much in the way of side effects. I got a bit more creaky in the morning so I took regular Claritin.” —pontiacpeggy
Read more in our anastrozole (Arimidex) discussion forum.
Paying for anastrozole
The cost of anastrozole may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use.
Note: Your insurance company may require you to get prior authorization before covering the medication.
ANI Pharmaceuticals has a program called Arimidex Patient Direct that can help.
Learn more about financial assistance and medicine cost-lowering tips.
— Last updated on February 1, 2025 at 5:36 PM
