Aromasin (chemical name: exemestane) is an aromatase inhibitor used to treat all stages of hormone receptor-positive breast cancer in post-menopausal women.

Aromasin (chemical name: exemestane) is an aromatase inhibitor used to:

  • to reduce the risk of hormone receptor-positive, early-stage breast cancer coming back (recurring) in post-menopausal women who have taken two to three years of tamoxifen; the women switch to Aromasin and complete 5 years of hormonal therapy after surgery

  • to treat advanced-stage breast cancer that has grown after tamoxifen treatment in post-menopausal women


How Aromasin works

Aromasin 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 or hormone receptor-positive breast cancer cells.

Aromasin will not work on hormone receptor-negative breast cancer.


Is Aromasin right for you?

Aromasin is used to treat post-menopausal women diagnosed with either early-stage or advanced-stage, hormone receptor-positive breast cancer.

Aromasin is not commonly used to treat pre-menopausal women.

Aromasin should not be taken with any medicine or supplement that contains estrogen.

You should not take Aromasin if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Aromasin may cause damage to developing embryos. You should use an effective non-hormonal type of birth control while you are taking Aromasin. Ask your doctor which type of non-hormonal birth control would be best for you. You should use the birth control for at least one month after your last dose of Aromasin.


What to expect during Aromasin treatment

Aromasin is a pill taken once per day. It is available as a generic medicine.

If you were diagnosed with early-stage breast cancer, you would switch to Aromasin after taking tamoxifen for two to three years, for a total of five continuous years of hormonal therapy treatment.

If you’ve been diagnosed with advanced-stage breast cancer, you would take Aromasin if the cancer grew after you were treated with tamoxifen. You would take Aromasin as long as you were getting benefits from the medicine.

There are certain medicines and supplements you should avoid if you’re taking Aromasin:

  • You should not take a type of medicine called a CYP3A4 inducer because it decreases the effects of Aromasin. This class of medicines includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy. St. John’s wort, an herbal supplement, also is considered a CYP3A4 inducer, so should not be taken with Aromasin.


Aromasin side effects

Like almost all breast cancer medicines, Aromasin can cause side effects, some of them severe.

The most common side effects of Aromasin are:

Other serious side effects Aromasin may cause include:

  • Bone loss: Because Aromasin 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 will likely monitor your bone density while you’re taking Aromasin.

  • Reduced vitamin D levels: Because many women diagnosed with early-stage breast cancer have low vitamin D levels, your doctor will likely monitor your levels while you’re taking Aromasin.

Research suggests that up to half of the women prescribed Aromasin or another hormonal therapy medicine stop taking the medicine early, in many cases because of troubling or painful side effects. Still, it’s very important to know that taking hormonal therapy for the prescribed amount of time can reduce the risk of recurrence by 50% and can reduce the risk of dying from breast cancer by about 30%.

If you’re having problematic side effects from taking Aromasin or another hormonal therapy medicine, talk to your doctor right away. There are steps you can take to ease some of the most common side effects:

  • medicines have been shown to reduce the number and severity of hot flashes

  • complementary and alternative therapies, such as acupuncture and mindfulness meditation, have been shown to ease pain, including joint pain

  • exercise has been shown to ease joint pain and increase bone density

You also may be able to switch to a different hormonal therapy medicine or take a different dose.


Paying for Aromasin

If your doctor prescribes Aromasin and you have problems paying for it or getting it covered by insurance, there is an Aromasin Savings Card that may be able to help you. The Pfizer RxPathways program is another option that connects eligible people to a range of assistance programs that offer insurance support, co-pay help, and medicines at a reduced cost.

Learn more about Paying for Your Care, including information on additional types of financial assistance and cost-lowering tips.


Aromasin (exemestane) prescribing information. Pfizer, USA. Available at:

— Last updated on July 27, 2022, 1:46 PM

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