--- title: 'Aromatase inhibitors (anastrozole, exemestane and letrozole)' url: https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/aromatase-inhibitors-anastrozole-exemestane-and-letrozole updated: 2026-03-30T07:36:54Z --- [Back to Hormone (endocrine) therapy](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy) 1. [Home](https://breastcancernow.org/) 2. [About breast cancer](https://breastcancernow.org/about-breast-cancer) 3. [Treatment](https://breastcancernow.org/about-breast-cancer/treatment) 4. [Hormone (endocrine) therapy](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy) Drug # 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. ## Speak to a nurse If you have any concerns about breast cancer, or just want to talk, our specialist nurses are here for you [0808 800 6000](tel:0808%20800%206000) We are open weekdays 9am to 4pm. Saturday 9am to 1pm ## In this section - 1. What are aromatase inhibitors? - 2. Is there a difference between letrozole, anastrozole and exemestane? - 3. Which aromatase inhibitor causes fewer side effects? - 4. How aromatase inhibitors work ## 1. What are aromatase inhibitors? Aromatase inhibitors are a type of hormone therapy drug used to treat breast cancer in women who have gone through a natural menopause (when periods stop). They can also be used in premenopausal women having ovarian suppression. The 3 aromatase inhibitor drugs are: 1. [Letrozole](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/letrozole-femara "Letrozole (Femara)") 2. [Anastrozole](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/anastrozole-arimidex "Anastrozole (Arimidex)") 3. [Exemestane](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/exemestane-aromasin "Exemestane (Aromasin)") Men with breast cancer may take an aromatase inhibitor, although another drug called [tamoxifen](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/tamoxifen "Tamoxifen") is more commonly used. Close Glossary term ## Hormone therapy Drugs that work in different ways to block the effect of oestrogen on cancer cells. Only used if the breast cancer is hormone receptor positive. Close Glossary term ## Ovarian suppression Sometimes called ovarian ablation. Stopping the ovaries producing oestrogen using surgery, drugs or radiotherapy. ## 2. Is there a difference between letrozole, anastrozole and exemestane? All 3 aromatase inhibitor drugs have similar effects and no 1 drug is better than another. If you have been offered an aromatase inhibitor, your treatment team will explain why they have recommended that particular drug. ## 3. Which aromatase inhibitor causes fewer side effects? Healthcare Information ### [Life during treatment](https://breastcancernow.org/about-breast-cancer/treatment/life-during-treatment) Going through breast cancer treatment can affect you physically and emotionally. Read our tips to help you cope. Like all drugs, aromatase inhibitors can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. The side effects of all the aromatase inhibitors are similar. However, some people may get on better with 1 drug than another. If you’re finding it hard to cope with side effects from an aromatase inhibitor, your treatment team may recommend changing to a different aromatase inhibitor or another hormone therapy drug. Find out more about coping with: - [Side effects of letrozole](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/side-effects-of-letrozole-femara "Side effects of letrozole (Femara)") - [Side effects of anastrozole](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/side-effects-of-anastrozole-arimidex "Side effects of anastrozole (Arimidex)") - [Side effects of exemestane](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/side-effects-of-exemestane-aromasin "Side effects of exemestane (Aromasin)") ## 4. How aromatase inhibitors work Drug ### [Hormone (endocrine) therapy](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy) Find out more about hormone (endocrine) therapy and what side effects you might have. Some breast cancers use oestrogen in the body to help them to grow. These are known as [oestrogen receptor positive or ER-positive breast cancers](https://breastcancernow.org/about-breast-cancer/diagnosis/hormone-receptors-and-breast-cancer/ "Hormone receptors and breast cancer"). Before the menopause, oestrogen is mainly made in the ovaries. The ovaries no longer make oestrogen after the menopause but some oestrogen is still made in other tissues. This is mainly in body fat and involves an a type of protein (enzyme) 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? Thank you for your feedback ### Was this helpful? Was this helpful? Yes No Please tell us what you liked about it. Answered my questions Easy to understand Right amount of information Reassuring We’re sorry you didn’t find this helpful. Please tell us why. Didn't answer my questions Hard to understand Too much information Upsetting If you have any more feedback, please let us know. Please do not include personal details and be aware we cannot respond to comments. If you have a question please call our helpline on 0808 800 6000. Send feedback Print this page ### Quality assurance Last reviewed in March 2026. The next planned review begins in March 2029. ![Trusted information creator. Patient Information Forum](https://breastcancernow.org/_content/BreastCancerNow.UmbracoComponents/images/quality-assurance-logo.png) ## Get support - ### Call our free helpline If you have any concerns about breast cancer, or just want to talk, our specialist nurses are here for you. [0808 800 6000](tel:0808%20800%206000) Lines open: Monday to Friday - 9am to 4pm; Saturday - 9am to 1pm - ### 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. 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