--- title: Letrozole (Femara) url: https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/letrozole-femara updated: 2026-03-31T08:23:24Z --- [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 # Letrozole (Femara) Find out more about letrozole (Femara), including what it is, when it's given and its side effects. ## 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 is letrozole? - 2. How letrozole works - 3. When is letrozole taken? - 4. How letrozole is taken - 5. How long will I have to take letrozole? - 6. Side effects of letrozole - 7. Stopping letrozole - 8. Other important information - 9. Further support ## 1. What is letrozole? Letrozole is a type of [hormone therapy](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy). You may also hear letrozole called by its brand name Femara. It’s used to treat breast cancer in women who have been through a natural menopause. It can also be used in women who haven’t been through the menopause who are having treatment to stop their ovaries working. Men with breast cancer may take letrozole, although another drug called [tamoxifen](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/tamoxifen "Tamoxifen")is more commonly used. ## 2. How letrozole works Some breast cancers use oestrogen in the body to help them 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 a type of protein (enzyme) called aromatase. Letrozole belongs to a group of drugs called [aromatase inhibitors](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/aromatase-inhibitors-anastrozole-exemestane-and-letrozole), which stop the aromatase enzymes from working. This means there’s less oestrogen in the body to help breast cancer cells grow. ## 3. When is letrozole taken? ### Primary breast cancer You may be offered letrozole if you have primary breast cancer. You usually take letrozole after surgery to reduce the risk of breast cancer returning in the same breast or spreading somewhere else in the body. This is known as adjuvant (additional) therapy. Occasionally, letrozole may be the first treatment for breast cancer. This may be when surgery is not appropriate or needs to be delayed. It’s sometimes given before surgery to shrink a larger breast cancer (known as neo-adjuvant or primary therapy). ### Breast cancer that has come back or spread You may be offered letrozole if you have: - Local recurrence - Locally advanced breast cancer - Metastatic (secondary) breast cancer ### Alongside ovarian suppression Letrozole is sometimes given alongside [ovarian suppression](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/ovarian-suppression-and-breast-cancer) if you haven’t been through the menopause. Close Glossary term ## Local recurrence ·       Breast cancer that has come back in the chest, breast or in the skin near the original site or scar. Close Glossary term ## Locally advanced breast cancer Abbreviated as LABC and sometimes called regional recurrence. Breast cancer that has come back and has spread to the chest wall or skin of the breast, or lymph nodes around the chest, neck and under the breastbone, but has not spread to other areas of the body. It cannot be removed by surgery. Close Glossary term ## Primary breast cancer Breast cancer that has not spread beyond the breast or the lymph nodes (lymph glands) under the arm (axilla). Close Glossary term ## Metastatic (secondary) breast cancer Breast cancer that has spread to other parts of the body such as the bones, lungs, liver or brain. Also called secondary breast cancer, metastases, advanced breast cancer, or stage 4 breast cancer. ## 4. How letrozole is taken You take letrozole as a tablet once a day, with or without food. You should take it at the same time every day. Some brands of letrozole contain a small amount of lactose. If you know you are lactose intolerant, discuss this with your treatment team or pharmacist. ### What happens if I miss a dose? If you miss a dose of letrozole, you do not need to take an extra dose the next day. The level of drug in your body will remain high enough from the day before. ## 5. How long will I have to take letrozole? 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. How long you take letrozole will depend on your individual situation. ### Primary breast cancer If you have primary breast cancer, you’ll usually take letrozole for 5 to 10 years. You may start taking letrozole after having taken a hormone therapy drug called [tamoxifen](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/tamoxifen) for a number of years. ### Breast cancer that has come back or spread For breast cancer that has come back or spread, you’ll have letrozole for as long as your treatment team feels you’re benefitting from it and any side effects are manageable. ## 6. Side effects of letrozole Like any drug, letrozole can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. ### [Side effects of letrozole (Femara)](https://breastcancernow.org/about-breast-cancer/treatment/hormone-endocrine-therapy/side-effects-of-letrozole-femara) Find out more about the side effects of letrozole (Femara). ## 7. Stopping letrozole ### Primary breast cancer Your treatment team will tell you when to stop taking letrozole. You won’t need to stop taking it gradually. Some people worry about stopping their treatment after 5 to 10 years. But there’s evidence that letrozole continues to reduce the risk of breast cancer coming back for many years after you stop taking it. However, not taking letrozole for the recommended time may increase the risk of your breast cancer coming back. If you’re thinking about stopping letrozole for any reason, talk to your treatment team first. It may be possible to change to another hormone therapy. If you’re worried about any long-term side effects after stopping letrozole, speak to your treatment team or GP. ### Metastatic (secondary) breast cancer Hormone therapy is a very common treatment for metastatic breast cancer. You’ll have letrozole for as long as your treatment team feels you’re benefitting from the drug and the side effects are manageable. If letrozole stops working, your treatment team may prescribe another hormone therapy drug. ## 8. Other important information ### Blood clots People with breast cancer have a higher risk of blood clots such as a DVT (deep vein thrombosis). If you have a DVT, there’s a risk part of the blood clot could break away and travel to the lung. This is known as a pulmonary embolism (PE). Blood clots can be life-threatening and should be treated quickly. i ### Blood clot symptoms **Contact your treatment team or go to your local A&E department straight away if you have any of the following symptoms:** - Pain in your arm or leg - Redness/discolouration of the skin of the arm or leg - Heat and swelling of the arm or leg - Swelling, redness or tenderness where a central line is inserted to give chemotherapy, for example in the arm, chest area or up into the neck - Shortness of breath that comes on suddenly - Pain or tightness in the chest - Unexplained cough or coughing up blood Some symptoms, such as redness and discolouration, may look different on different skin tones. Find out more about [blood clots](https://breastcancernow.org/about-breast-cancer/treatment/blood-clots/ "Blood clots"). ### Taking letrozole with other drugs If you’re taking any other prescribed or over-the-counter medicines, check with your treatment team or pharmacist if you can take these with letrozole. Do not take other drugs containing oestrogen, such as hormone replacement therapy (HRT), while you’re taking letrozole, as this may interfere with its effectiveness. ### Herbal medicines and supplements Many people consider taking herbal products or supplements while having treatment for breast cancer. However, the exact effect and safety of taking these after a diagnosis of breast cancer is not fully understood. Ask your treatment team or pharmacist before taking herbal products or supplements. You can read more about supplements in our information on [healthy eating after breast cancer treatment](https://breastcancernow.org/about-breast-cancer/life-after-treatment/your-body-after-breast-cancer-treatment/healthy-eating-after-breast-cancer-treatment). ### Sex, contraception and pregnancy You’re advised not to become pregnant while having treatment because letrozole can harm a developing baby. If you have not been through the menopause, talk to your team about the most suitable method of contraception for you. It’s still possible to become pregnant even if your periods are irregular or have stopped naturally or because of treatment for breast cancer. ### Fertility The impact of letrozole on [fertility](https://breastcancernow.org/about-breast-cancer/primary-breast-cancer/breast-cancer-in-younger-women/fertility-and-breast-cancer-treatment) is not currently known. It’s important to discuss any fertility concerns with your treatment team before you begin your treatment. If you’re planning to get pregnant after you have finished taking letrozole, or want to take a break from letrozole to become pregnant, speak to your treatment team. ### Breastfeeding Breastfeeding is not recommended while having letrozole. This is because there’s a risk the drugs could be passed on through breast milk. ## 9. Further support If you have any worries or questions about letrozole, you can call our helpline free on **0808 800 6000** to talk through your concerns. You can also email **nurse@breastcancernow.org** You can find out more about our support services below. ### 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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