The short answer
Femara (Letrozole) is a hormone therapy for breast cancer. It lowers the body's estrogen by blocking an enzyme (aromatase) that makes it, which can slow the growth of estrogen-fueled breast cancers after menopause. It is used to help treat hormone-receptor-positive breast cancer in postmenopausal women, and is usually given as one pill taken by mouth each day. Like all cancer medicines it can cause side effects; this page explains the common ones and the warning signs to report. It is educational only and not a substitute for your care team's advice.
Femara is the brand name; its generic name is letrozole.
It is a hormone therapy for breast cancer — it lowers the body's estrogen by blocking an enzyme (aromatase) that makes it, which can slow the growth of estrogen-fueled breast cancers after menopause.
It is used to help treat hormone-receptor-positive breast cancer in postmenopausal women.
It is usually given as one pill taken by mouth each day.
Choose how you want to read this
The whole article, with every detail and caution.
This page is for women who have been prescribed letrozole (Femara) for breast cancer, and their families. It covers how the drug works, when it is used, common side effects, and when to get help.
Why it only works after menopause
Femara is the brand name. Letrozole is the generic name. It blocks aromatase, the enzyme (a protein that speeds up a chemical reaction) that builds estrogen out of other hormones in fat, muscle and skin.
The FDA label covers postmenopausal women. Ask your oncologist if you have questions about whether it fits your situation.
The usual amount is one 2.5 mg tablet a day, with or without food. For people with cirrhosis or severe liver problems, the label says one tablet every other day. Take it exactly as your own prescription and pharmacy label say. If those disagree with this paragraph, call your team rather than adjusting anything yourself.
When it is prescribed in breast cancer
The FDA label lists three uses.
- After surgery for hormone receptor positive early breast cancer.
- After 5 years of tamoxifen, as extended treatment for early breast cancer.
- For advanced breast cancer that is hormone receptor positive or of unknown status. The label covers first treatment, and treatment after disease progression following antiestrogen therapy.
Joint and muscle pain
The FDA label lists joint pain and bone pain among the most common side effects. If pain is a problem, tell your team before you decide on your own to stop. They can talk with you about your options.
Bone health over years of treatment
The label says letrozole may lower bone density and that monitoring should be considered. In one large trial, bone fractures were reported in 14.7% of people on letrozole and 11.4% on tamoxifen. The label also says cholesterol may rise and that monitoring should be considered. Ask your team how your bones and cholesterol will be checked.
Staying with it for the full course
The label says the best length of treatment is not known. In the main trials, the median was about 5 years. Ask your team how long you should take it. Tiredness, dizziness and sleepiness are listed on the label, so take care driving and using machinery until you know how it affects you. Hot flashes and sweating are also common side effects.
If you have missed doses, say so honestly. Your team would rather solve the reason than assume you are taking it.
When to get help sooner
- Call 911 or go to an emergency department if a fall or even a minor stumble leaves you unable to weight-bear, or your hip, wrist or back is suddenly and severely painful. The label reports bone fractures and lower bone density with letrozole. Do not drive yourself.
- Call your care team within a day or two if joint or muscle pain is bad enough that you are thinking of stopping the tablets, or if dizziness or sleepiness is making driving feel unsafe.
There is no need to wait for a review appointment to raise either of these. Both usually have a fix.
Sources
https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=82b77d74-085f-45ac-a7dd-1f5c038bf406
https://www.cancer.gov/about-cancer/treatment/drugs/letrozole
Common questions
What is Femara?
Femara (Letrozole) is a hormone therapy for breast cancer. It lowers the body's estrogen by blocking an enzyme (aromatase) that makes it, which can slow the growth of estrogen-fueled breast cancers after menopause. It is used to help treat hormone-receptor-positive breast cancer in postmenopausal women.
How is Femara given?
It is usually given as one pill taken by mouth each day. The FDA label gives the usual dose as one 2.5 mg tablet once a day, with or without food. The label says the best length of treatment is not known. In the main trials, the median was about 5 years. Take it as prescribed and talk with your team before stopping.
What are the common side effects of Femara?
The FDA label lists hot flashes, joint pain, flushing, weakness, swelling, headache, dizziness, higher cholesterol, increased sweating and bone pain among the most common side effects. It also warns of lower bone density, higher cholesterol, and tiredness, dizziness or sleepiness. Not everyone gets them. Tell your care team about anything new or worsening.
Does Femara cure cancer?
That depends on the person, the cancer type, and its stage. For some people a medicine like this can control cancer for a long time or be part of a curative plan; for others the goal is to slow the cancer or ease symptoms. Your care team can explain the goal in your situation.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-07-14 what this meansLast updated: 2026-09-29Next planned review: 2027-01-14
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Editorial review complete. This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
Knowledge check
0 of 2 answered
This self-assessment checks understanding of educational content only. It is not medical advice.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.