Exemestane (Aromasin): What to Expect, Side Effects, and More
Exemestane (brand name: Aromasin) is an aromatase inhibitor used:
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
to treat advanced-stage breast cancer that has grown after tamoxifen treatment in post-menopausal women
See Aromasin prescribing information.
How exemestane 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 of hormone receptor-positive breast cancer cells.
What to expect during exemestane treatment
Aromasin is a pill taken once a day. The typical dose is 25 mg per day.
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. Switching to an aromatase inhibitor like Aromasin tamoxifen treatment can lead to a greater reduction in recurrence risk. You may be advised to continue Aromasin even after you have completed five years of total therapy.
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.
Exemestane side effects
Like almost all breast cancer medicines, exemestane can cause side effects, some of them severe.
The most common side effects of Aromasin are:
Other serious side effects exemestane 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 and may recommend additional medications to increase your bone density or to prevent further bone loss.
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. If you have a vitamin D deficiency, your doctor may also recommend a supplement.
You should not take Aromasin if you’re pregnant or breastfeeding.
Aromasin drug interactions
You should not take CYP3A4 inducers, because they decrease 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, is also considered a CYP3A4 inducer.
What happens when you stop taking exemestane?
Stopping Aromasin earlier than recommended by your doctor may increase your risk of the cancer coming back or spreading.
Some side effects may persist even after stopping the medication.
If you’re considering refusing or stopping 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.
Real patient reviews
Members of our community discuss their experiences with Aromasin 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 have tried Aromasin and had massive migraines.” — kyliet
“I was on Aromasin for 5 years after 2.5 years of tamoxifen. I had NO perceptible side effects apart from hair thinning.” — sam52
“[I] had insomnia, joint pain, anxiety, depression, [and] memory and cognitive issues on Aromasin.” — karen1956
Read more in our Aromasin discussion forum.
Paying for exemestane
The cost of Aromasin 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 Aromasin.
Learn more about financial assistance and medicine cost-lowering tips.
— Last updated on June 2, 2025 at 3:57 PM
