What are aromatase inhibitors?

Aromatase inhibitors are a group of drugs used to treat breast cancer in women who have been through the menopause.

The three aromatase inhibitor drugs are:

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

Is there a difference between letrozole, anastrozole and exemestane?

All three 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.

Which aromatase inhibitor causes the fewest side effects?

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

People often ask if one drug causes fewer side effects than the others. 

The side effects of all three 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:

How aromatase inhibitors work

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

Some breast cancers are stimulated to grow by the hormone oestrogen (known as oestrogen receptor positive or ER+ breast cancer). 

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 encourage breast cancer cells to grow.

Last reviewed: February 2019
Next planned review begins 2021

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