Letrozole
Pronunciation: pronunciation varies by local usage.
- Generic name
- letrozole
- Brand names
- FEMARA
- Drug class
- Aromatase inhibitor
- Form
- Film-coated tablet
- Route
- Oral
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What letrozole is and how it works
Letrozole is an oral aromatase inhibitor used to treat hormone receptor-positive breast cancer in postmenopausal women. (1)
It is prescribed as adjuvant therapy, extended adjuvant therapy after tamoxifen, or for advanced disease. A specialist determines eligibility, treatment duration, and any dose adjustments.
Mechanism of action: how letrozole works
Letrozole is an oral aromatase inhibitor used in postmenopausal women with hormone receptor-positive breast cancer. (1)
What letrozole is used for
Adjuvant treatment of early breast cancer
Letrozole is used as initial adjuvant therapy in postmenopausal women with hormone receptor-positive early breast cancer following surgery. (1)
Extended adjuvant treatment after tamoxifen
It is used for extended adjuvant treatment of early breast cancer in postmenopausal women who have completed 5 years of standard adjuvant tamoxifen therapy. (1)
First-line advanced breast cancer
Letrozole is indicated for first-line treatment of postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer. (1)
Second-line advanced breast cancer
It is also indicated for treatment of advanced breast cancer in postmenopausal women with disease progression following antiestrogen therapy. (1)
Before taking letrozole
Do not take / not appropriate for
- Tell your doctor if you are pregnant, think you may be pregnant, or intend to become pregnant. Letrozole is contraindicated in pregnancy because it can cause serious harm to the unborn baby; your doctor will advise on next steps. (all patients) (1)
- Tell your doctor if you have had a severe allergic reaction (hypersensitivity) to letrozole or any of the tablet ingredients; your doctor will confirm whether letrozole is appropriate for you. (all patients) (1)
Tell your clinician about
- All medical conditions, especially liver disease or reduced liver function, high cholesterol, or known bone thinning (osteoporosis) or fractures.
- Whether you have gone through menopause; the reviewed US-label breast-cancer indications for letrozole are for postmenopausal women.
- If you are able to become pregnant, or if you are breastfeeding or plan to breastfeed.
- All medicines you take, including prescription and over-the-counter drugs, especially tamoxifen, warfarin, or other anticancer treatments.
- If you experience unusual tiredness or dizziness that could affect your ability to drive or operate machinery.
How to take letrozole
- The usual dose is one 2.5 mg tablet taken once daily by mouth, with or without food.
- Do not change the dose or take an extra tablet on your own. Any decision about changing the dose or continuing treatment is made by the prescribing specialist.
- If you have severe liver problems, your doctor will prescribe a different dosing schedule (for example, one tablet every other day) based on your medical condition.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
No specific missed-dose guidance was found in the reviewed prescribing information. Contact your prescriber for individualised instructions.
Overdose
The highest single dose reported was 62.5 mg, with no serious adverse reactions. Seek urgent clinician advice for a suspected overdose; supportive care and any further management are clinician-managed. (1)
Side effects
This summary is based on the adjuvant breast cancer trial. Effects may differ in other treatment settings.
Hot flashes
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Tell your treatment team about this. (1)
Joint pain or arthritis
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Tell your doctor about this. (1)
High cholesterol (hypercholesterolemia)
What to notice: Usually has no symptoms; detected by a blood test.
What to do: Your doctor will monitor your cholesterol levels regularly during treatment. (1)
Night sweats
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Tell your team about this. (1)
Fatigue and dizziness
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Use caution when driving or operating machinery until you know how letrozole affects you. (1)
Fluid retention (edema)
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Tell your prescriber about this. (1)
Bone fractures
What to notice: The reviewed label lists this as a common adverse reaction without a specific patient-facing symptom description beyond the reaction name.
What to do: Bone density monitoring is recommended. (1)
Signs of possible bone thinning or fracture
What to notice: Not established from the sources reviewed: a specific patient-facing symptom list was not established in the sources reviewed for this page beyond the named risks of decreased bone mineral density and fracture.
What to do: Contact your treatment team for assessment and possible bone density testing. (1)
Severe fatigue or dizziness affecting daily activities
What to notice: Not established from the sources reviewed: a specific patient-facing symptom list was not established in the sources reviewed for this page beyond fatigue and dizziness as named adverse reactions.
What to do: Speak with your prescriber; avoid driving or hazardous activities until you have been evaluated. (1)
Serious warnings
Embryo-fetal toxicity (pregnancy risk) — contraindication
Action: Pregnancy is a contraindication for letrozole. Obtain a pregnancy test before initiating therapy, and use effective contraception during treatment and for 3 weeks after the last dose. Contact your doctor immediately if you are or may be pregnant, so they can advise on next steps. (1)
Decreased bone mineral density and fracture risk — warning
Symptoms: Not established from the sources reviewed: a specific patient-facing symptom list was not established in the sources reviewed for this page beyond the named risks of decreased bone mineral density and fracture.
Action: Regular bone density monitoring is recommended. Tell your doctor about any new bone symptoms. (1)
Hypercholesterolemia (high cholesterol) — warning
Symptoms: Generally no noticeable symptoms; detected by blood tests.
Action: Serum cholesterol should be checked before and during treatment. (1)
Fatigue and dizziness affecting driving or operating machinery — caution
Symptoms: Not established from the sources reviewed: a specific patient-facing symptom list was not established in the sources reviewed for this page beyond fatigue and dizziness as named adverse reactions.
Action: Exercise caution when driving or operating machinery if you are affected. Consult your doctor if symptoms persist. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Tamoxifen | Tamoxifen reduces letrozole plasma levels by about 38%, but this does not appear to impair letrozole's effectiveness. | Your doctor will decide the appropriate sequencing or combination; do not change your tamoxifen use without guidance. (1) |
| Cimetidine and warfarin | No clinically significant interactions have been observed with cimetidine or warfarin. | Inform your prescriber about all your medications. (1) |
| Other anticancer agents | Limited clinical experience is available on the concurrent use of letrozole with other anticancer medicines. | Give your doctor a complete list of all cancer treatments you are receiving. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Letrozole can cause fetal harm and is contraindicated during pregnancy. Postmarketing reports have included spontaneous abortion and birth defects. Obtain a pregnancy test before initiating therapy, and use effective contraception during treatment and for 3 weeks after the last dose. (1)
Breastfeeding
Breastfeeding is not recommended during letrozole treatment and for 3 weeks after the final dose. (1)
Pediatric use
Safety and effectiveness have not been established in children and adolescents. Animal studies have shown adverse effects on bone growth and development at clinically relevant exposures. (1)
Hepatic impairment (liver problems)
For patients with cirrhosis or severe hepatic dysfunction, the recommended dose is 2.5 mg every other day. Liver function monitoring is recommended if hepatic impairment is present. (1)
Renal impairment (kidney problems)
No dose adjustment is needed in patients with a creatinine clearance of 10 mL/min or greater. (1)
Monitoring
Before starting
- Confirm postmenopausal status.
- Obtain a pregnancy test in women of reproductive potential.
- Assess baseline bone mineral density.
- Check serum cholesterol levels.
- Evaluate liver function if hepatic impairment is suspected or known.
- Review all concurrent medications, especially tamoxifen and anticoagulants.
During treatment
- Bone mineral density monitoring is recommended, given the increased fracture risk.
- Serum cholesterol monitoring is recommended.
- Liver function monitoring is recommended if hepatic impairment is present.
- Pregnancy status is monitored in women of reproductive potential.
- Ask about adverse effects such as fatigue, dizziness, joint pain, or edema.
Storage
Specific storage conditions were not reviewed in this pass. Refer to the product packaging or ask your pharmacist.
Professional information
Clinician-facing context only. Use the current local label and guidelines for complete prescribing decisions.
United States (per FDA label)
Indication: All approved letrozole indications
Dose summary: 2.5 mg orally once daily with or without food. In patients with cirrhosis or severe hepatic dysfunction, the dose is reduced to 2.5 mg every other day.
Renal context: No dose adjustment is necessary for creatinine clearance ≥10 mL/min. (1)
Hepatic guidance
Dose adjustment is required for severe hepatic impairment as described in regional dosing; hepatic function should be monitored.
Overdose note
The highest reported single dose was 62.5 mg with no serious adverse effects. The treating clinician will decide on supportive care, vital-sign monitoring, and whether emesis is appropriate. (1)
Frequently asked questions
Can premenopausal women take letrozole for breast cancer?
The reviewed US-label breast-cancer indications for letrozole are for postmenopausal women. If you are not sure about your menopausal status, your doctor will assess it before prescribing. (1)
Will letrozole weaken my bones?
Letrozole can cause a decrease in bone mineral density and an increased risk of fractures. Regular bone density monitoring is recommended, and your doctor can advise on ways to protect your bones. (1)
What should I do if I miss a dose?
The product label does not give specific missed-dose instructions. Contact your prescriber for advice based on your individual situation.
What is the mechanism of action of letrozole?
Letrozole is an oral aromatase inhibitor used in postmenopausal women with hormone receptor-positive breast cancer. (1)
What is the generic name of Letrozole?
The generic name is letrozole. It is sold under brand names including FEMARA. (1)
What class of drug is letrozole?
Letrozole is classed as: Aromatase inhibitor. (1)
References
- FEMARA (letrozole) tablet, film coated — prescribing informationU.S. Food and Drug Administration · United States · dated Not established (label revision date not identified; accessed 2026-08-05) · accessed 2026-08-05 · source 1
- LETROZOLE TABLET [BRECKENRIDGE PHARMACEUTICAL, INC.] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 2
- Letrozole — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 3
- Letrozole — FDA approval record (Drugs@FDA ANDA090934)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- letrozole — RxNorm normalized drug concept (RXCUI 72965)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient letrozole names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Femara2.5 mg · novartis pharmaceuticals corporation
Canada
- FEMARA
- MED-LETROZOLE
- ACH-LETROZOLE
- ZINDA-LETROZOLE