Pros and Cons of Arimidex vs. Aromasin for Breast Cancer

Breast cancer is one of the most common cancers affecting women — occurring in nearly 13% within this group. A healthcare provider considers many factors when selecting a treatment regimen, including how advanced the cancer is, if the person has certain genetic changes, and if the cancer cells use the body’s natural hormones to grow.

In 2017, more than 250,000 people were diagnosed with breast cancer in the U.S. Of those, the most common subtype is known as Luminal A breast cancer and accounts for about 88% of all breast cancer. This form of breast cancer is sensitive to hormones in the body — called hormone receptor-positive (HR+) — but is negative for a protein called HER2. This subtype can be further divided, based on whether the cancer cells are sensitive to estrogen or progesterone.

For people with estrogen-sensitive breast cancer — estrogen receptor-positive (ER+) breast cancer — treatments typically focus on lowering the amount of estrogen in the body. While there are various treatment options available across several medication classes, two commonly prescribed medications are anastrozole (Arimidex) and exemestane (Aromasin).

In this article, we’ll compare how these two medications work for this type of breast cancer and what you can expect if your healthcare provider has prescribed one of them for you.

When are Arimidex or Aromasin typically prescribed?

As mentioned above, ER+ breast cancer is sensitive to estrogen and uses this hormone to grow. When people have this type of cancer, medications that help lower estrogen levels in the body can help limit or cut off the supply of this hormone to the cancer cells. 

Anastrozole and exemestane are known as aromatase inhibitors (AIs). AIs are one class of medications that can be used to treat ER+ breast cancer. They work by blocking aromatase, an enzyme (protein) crucial for turning androgens, such as testosterone, into estrogen in the body.

Medications like anastrozole and exemestane are most often prescribed for people who have gone through menopause. This is because the primary way the body makes estrogen changes after menopause. Before menopause, the body makes most of its estrogen in the ovaries. After menopause, estrogen is made from fat cells using aromatase. So taking an AI will help prevent aromatase from creating estrogen — thus cutting off the cancer cells’ main source of the hormone.

Anastrozole and exemestane are both used to treat ER+ breast cancers. However, their FDA approvals are slightly different.

Anastrozole is approved as a first-choice medication for HR+ breast cancer in people who have gone through menopause. Exemestane is approved for ER+ breast cancer in people who have gone through menopause and have already tried a different breast cancer medication called tamoxifen without success.

The National Comprehensive Cancer Network (NCCN) — an organization that helps establish clinical practice standards for cancer specialists — recommends these two medications or another breast cancer medication called tamoxifen be used as adjuvant therapy. Adjuvant therapy is when you use medications, chemotherapy, or radiation therapy after an initial treatment or surgical procedure to help better eliminate cancer cells.

Who should not take Arimidex or Aromasin?

Anastrozole and exemestane are not effective in treating estrogen-receptor negative (ER-) breast cancers, including triple-negative breast cancer — breast cancer that is not sensitive to estrogen or progesterone and lacks the HER2 protein. Since these breast cancer types don’t use estrogen to grow, blocking estrogen production doesn’t help treat them.

AIs also aren’t approved for people who haven’t gone through menopause. This is because the ovaries are still producing estrogen. When people who haven’t gone through menopause take AIs, the brain sends signals to produce even more estrogen — which can prevent the medication from working properly. 

If your healthcare provider has decided to have you try an AI and you haven’t gone through menopause yet, it would most likely be given in combination with a luteinizing hormone-releasing hormone (LHRH) analog. These medications signal your ovaries to stop producing estrogen, helping AIs to be more effective than they would be alone.

If you are prescribed this combination, your healthcare provider may discuss birth control options and ask whether you’re currently nursing. This is because you shouldn’t take medications like anastrozole or exemestane if you are pregnant, trying to become pregnant, or nursing. These medications may be harmful to an unborn baby or nursing infant.

What are the typical dosages for Arimidex and Aromasin?

Both anastrozole and exemestane are available as oral tablets taken once daily. The usual dose for anastrozole is 1 mg taken with or without food. Exemestane is commonly dosed at 25 mg and best taken after a meal.

How long do you have to take Arimidex or Aromasin?

According to the American Society of Clinical Oncology (ASCO), AIs like anastrozole or exemestane should be taken by people who have gone through menopause for up to 5 years following a mastectomy — surgery that removes part of all of the breast(s).

However, in some cases, ASCO recommends that some people who also have cancer cells in their lymph nodes (called node-positive cancer) that have gone through menopause with early-stage HR+ breast cancer can be treated with AIs for up to 10 years after surgery. This is generally known as extended adjuvant hormonal therapy.

Which is better: Arimidex or Aromasin?

Both anastrozole and exemestane are effective in treating ER+ breast cancer. 

A randomized clinical trial comparing anastrozole, exemestane, and letrozole (Femara) — another AI — showed that all three medications are similarly effective in treating breast cancer. Just under 90% of people in the study had no signs or symptoms (called disease-free survival) of breast cancer during the 5 years the study was being performed, regardless of which medication they took.

Another study also found anastrozole and exemestane to be similarly effective. Approximately 91% of people taking either medication had disease-free survival after 4 years.

Since people may respond differently to these medications, make sure to talk to your healthcare provider about how you are responding to the medication and any side effects you are experiencing.

What side effects are associated with Arimidex and Aromasin?

Since they are both AIs, anastrozole and exemestane can cause similar side effects. Many of these side effects are caused by the medications’ estrogen-lowering abilities.

Common side effects may include the following:

• Hot flashes

• Muscle or joint pain

• Weakness

• Vaginal dryness

• Pain during sex

• Weakened bones

• High cholesterol or blood pressure

• Insomnia

• Nausea

Estrogen plays an important role in regulating bone health. Since AIs lower estrogen levels, they may cause more rapid bone loss and raise the risk of broken bones. Before starting AI treatment, your healthcare provider will assess your current bone health and may recommend taking a bone-strengthening medication. Medications, such as denosumab (Prolia) and zoledronic acid (Reclast), can be helpful in treating or preventing bone loss caused by AIs. 

The likelihood of some of these potential side effects can differ between medications. One small study suggests that exemestane may be more likely to cause high cholesterol compared to anastrozole. On the flip side, anastrozole may be more damaging to bone health than exemestane.

Taking AIs can sometimes also cause liver enzymes (liver proteins) to rise — a potential sign of liver damage. In very rare cases, AIs have been associated with severe liver inflammation (swelling). Therefore, it’s important to let your healthcare provider know if you experience any signs of liver damage while taking an AI.

Signs of liver damage can include:

• Yellow eyes or skin (called jaundice)

• Pain in the upper-right area of your abdomen

• Swelling of the abdomen

• Nausea or vomiting that doesn’t go away

Your healthcare provider will take these differences, side effects, and your medical history into account when choosing which AI to prescribe for you.

Can you switch from Arimidex to Aromasin or vice versa?

Everyone’s experience with side effects is unique and may differ from one AI to another. For instance, people experiencing muscle pain, swelling, or joint pain from one AI may benefit from switching to a different medication in this class.

As mentioned above, both anastrozole and exemestane are similarly effective for treating ER+ breast cancer. So, switching between them shouldn’t affect how your breast cancer is being treated. If you’re experiencing side effects from your medication, make sure to discuss what you’re feeling with your healthcare provider.

How to save on Arimidex and Aromasin

Arimidex and Aromasin are available as brand-name medications. But you can also find them as lower-cost generics. GoodRx can help you navigate the many ways to save on your prescription.

• Save with GoodRx: GoodRx can help you save over 90% off the average retail price of the generic versions of Arimidex and Aromasin. Generic anastrazole’s price at certain pharmacies is as low as $9.74 with a free GoodRx discount. Generic exemestane’s price at certain pharmacies is as low as $16.20 with a free GoodRx discount.

• Use exclusive savings: Anyone with a valid prescription, regardless of insurance status, can use GoodRx to purchase a 30-day supply of Arimidex at an exclusive cash price of $298.80.

• Save with a copay savings card: If you have insurance, you may be eligible to pay as little as $60 (30-day supply) or $180 (90-day supply) for Arimidex using the manufacturer’s Arimidex Patient Direct program. This program also offers home delivery.

• Save with patient assistance programs: If you’re uninsured or underinsured, you may be eligible for Aromasin's patient assistance program, which offers the medication at no charge.

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Written by:

Kevin Le, PharmD, BCPS, BCPPS

Kevin Le, PharmD, BCPS, BCPPS is a clinical pharmacy specialist in solid organ transplant at Ann & Robert H. Lurie Children’s Hospital of Chicago. He has been working as a pediatric pharmacist since 2016.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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