Contact our breast care nurses 0808 800 6000

Aromatase inhibitors (anastrozole, exemestane and letrozole)

Find out about aromatase inhibitors, a type of hormone therapy normally used to treat breast cancer in women who have gone through the menopause, including side effects and how they work.

1. What are aromatase inhibitors?

Aromatase inhibitors are a type of drug used to treat breast cancer in women who have gone through a natural menopause (when periods stop). It can also be used in premenopausal women having .

The three aromatase inhibitor drugs are:

  1. Letrozole 
  2. Anastrozole 
  3. Exemestane 

Men with breast cancer may be given an aromatase inhibitor, although another drug called tamoxifen is more commonly used.

2. Is there a difference between letrozole, anastrozole and exemestane?

All 3 aromatase inhibitor drugs have similar effects and no one drug is better than another.

If you have been offered an aromatase inhibitor, your specialist will explain why they have recommended that particular drug.

3. Which aromatase inhibitor causes fewer side effects?

Like all drugs, aromatase inhibitors can cause side effects. Everyone reacts differently to drugs and it’s not possible to predict how any of the drugs will affect an individual.

The side effects of all 3 drugs are similar. However, some people may get on better with one drug than another. 

If you’re finding it hard to cope with side effects from one aromatase inhibitor, your specialist may recommend changing to a different aromatase inhibitor or another hormone therapy drug. 

Find out more about coping with:

4. How aromatase inhibitors work

Aromatase inhibitors help reduce the amount of oestrogen made in the body. 

Some breast cancers use oestrogen in the body to help them to grow. These are known as oestrogen receptor positive or ER+ breast cancers.

Before the menopause, oestrogen is mainly produced in the ovaries. After the menopause, the ovaries no longer produce oestrogen, but some oestrogen is still made in body fat. This process involves an enzyme (a type of protein) called aromatase. 

Aromatase inhibitors stop this enzyme from working. This means there’s less oestrogen in the body to help breast cancer cells to grow.

Was this helpful?

Was this helpful?
Please tell us what you liked about it.
Please tell us why.
We’re sorry you didn’t find this helpful.
Please do not include personal details and be aware we cannot respond to comments.

Quality assurance

This information was published in April 2022. We will revise it in April 2024.

Get support

  • support-cta-icon-telephone

    Call our free helpline

    If you have any concerns about breast cancer, or just want to talk, our specialist nurses are here for you.

    Lines open: Monday to Friday - 9am to 4pm; Saturday - 9am to 1pm

  • support-cta-icon-email

    Explore ways to talk to our nurses

    It can be difficult to talk to someone in person about breast cancer concerns. Explore other ways you can ask a question.

Share this page