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What happens when you stop taking Arimidex?

Medically reviewed by Carmen Pope, BPharm. Last updated on April 28, 2025.

Official Answer by Drugs.com

Arimidex (anastrozole) is a medication that is used to treat breast cancer in postmenopausal women. In most cases, Arimidex is taken for five years, although some women may take it for a shorter period.

Many women worry that stopping Arimidex after five years will cause their cancer to come back; however, the International Breast Cancer Intervention Study II (IBIS-II) Prevention trial reports that:

Once your treatment team has decided that you can stop taking Arimidex, you can stop it completely; you won’t need to taper down the dose gradually.

How long do side effects continue once Arimidex is stopped?

Many side effects of Arimidex will improve within a couple of weeks of stopping arimidex; however, some may persist long term. No new side effects have been reported in clinical trials after stopping Arimidex.

Side effects that should resolve quickly include:

Side effects that may persist for a few months, or that may still require medications to treat them include:

Unfortunately, no formal clinical studies have been done investigating the persistence of side effects from Arimidex.

How long does Arimidex last in your body for?

The half life of Arimidex is 30 to 60 hours. Generally it takes four to five half-lives for a drug to be eliminated from the body, so in the case of Arimidex this would be 150 to 300 hours, or six to 12 days.

How does Arimidex work?

The growth of many cancers of the breast is stimulated or maintained by estrogens. Arimidex lowers estrogen levels by preventing the synthesis of estrogen from adrenal androgens (primarily androstenedione and testosterone).

It does this by inhibiting the enzyme aromatase, which converts these androgens into estrogen. This slows the growth of tumors that require estrogen to grow. Arimidex is selective too which means that it only affects blood estradiol concentrations, and has no effect on the formation of adrenal corticosteroids or aldosterone.

References

Read next

What is Veridex used for?

Veridex, a brand name drug from Turkey, has been reported as containing the breast cancer medicine anastrozole. Anastrozole is known as Arimidex in the U.S. Continue reading

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