Letrozole: uses, dosing, side effects & brands
Letrozole is an aromatase inhibitor sold in the U.S. under 2 brand and generic names, for breast neoplasms. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Drug class
- Aromatase Inhibitor
- Treats
- Breast Neoplasms
- Available as
- Tablet
- Sold as
- 2 products — Letrozole and Femara
- Prescription?
- Prescription only
- Generic available?
- Yes
- Half-life
- about 2 days (terminal elimination half-life)
- What the pharmacy pays
- about $4 for a 30-count supply — not your price
How letrozole is dosed
From the FDA label for Femara (application NDA020726). Other letrozole products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.
Femara tablets are taken orally without regard to meals ( 2 ): Recommended dose: 2.5 mg once daily. ( 2.1 ) Patients with cirrhosis or severe hepatic impairment: 2.5 mg every other day. ( 2.5 , 5.3 ) 2.1 Recommended Dose The recommended dose of Femara is one 2.5 mg tablet administered once a day, without regard to meals. 2.2 Use in Adjuvant Treatment of Early Breast Cancer In the adjuvant setting, the optimal duration of treatment with letrozole is unknown. In both the adjuvant study and the post approval adjuvant study, median treatment duration was 5 years. Treatment should be discontinued at relapse [ see Clinical Studies (14.1) ] . 2.3 Use in Extended Adjuvant Treatment of Early Breast Cancer In the extended adjuvant setting, the optimal treatment duration with Femara is not known. The planned duration of treatment in the study was 5 years. In the final updated analysis, conducted at a median follow-up of 62 months, the median treatment duration for Femara was 60 months. Seventy-one percent (71%) of patients were treated for at least 3 years and 58% of patients completed at least 4.5 years of extended adjuvant treatment. The treatment should be discontinued at tumor relapse [see Clinical Studies (14.2)] . 2.4 Use in First and Second-Line Treatment of Advanced Breast Cancer In patients with advanced disease, treatment with Femara should continue until tumor progression is…
Letrozole side effects
The following adverse reactions are discussed in greater detail in other sections of the labeling. Bone effects [see Warnings and Precautions (5.1)] Increases in cholesterol [see Warnings and Precautions (5.2)] Fatigue and Dizziness [see Warnings and Precautions (5.4)] The most common adverse reactions (greater than 20%) were hot flashes, arthralgia; flushing, asthenia, edema, arthralgia, headache, dizziness, hypercholesterolemia, sweating increased, bone pain; and musculoskeletal. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Novartis Pharmaceuticals Corporation at 1-888-669-6682 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reactions rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Adjuvant Treatment of Early Breast Cancer In study, BIG 1-98, the median treatment duration of adjuvant treatment was 60 months and the median duration of follow-up for safety was 96 months for patients receiving Femara and tamoxifen. Certain adverse reactions were prospectively specified for analysis (see Table 1), based on the known pharmacologic properties and side effect profiles of the two drugs. Adverse reactions were analyzed irrespective of…
Who shouldn’t take letrozole
Pregnancy: Letrozole can cause fetal harm [see Use in Specific Populations (8.1)] . Known hypersensitivity to the active substance, or to any of the excipients [see Adverse Reactions (6)] . Pregnancy. ( 4 ) Known hypersensitivity to the active substance, or to any of the excipients. ( 4 )
Letrozole drug interactions
Tamoxifen Coadministration of Femara and tamoxifen 20 mg daily resulted in a reduction of letrozole plasma levels of 38% on average (Study P015). Clinical experience in the second-line breast cancer trials (AR/BC2 and AR/BC3) indicates that the therapeutic effect of Femara therapy is not impaired if Femara is administered immediately after tamoxifen. Cimetidine A pharmacokinetic interaction study with cimetidine (Study P004) showed no clinically significant effect on letrozole pharmacokinetics. Warfarin An interaction study (P017) with warfarin showed no clinically significant effect of letrozole on warfarin pharmacokinetics. Other Anticancer Agents There is no clinical experience to date on the use of Femara in combination with other anticancer agents.
Every letrozole product we track (2)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
| # | Drug | Rating | Type | Form | Generic? | Pharmacy pays | |
|---|---|---|---|---|---|---|---|
| 1 | 72/100 | Prescription | Tablet | Generic | $4 | View → | |
| 2 | 70/100 | Prescription | Tablet | Generic | $4 | View → |
What letrozole pills look like
Imprint codes, colour and shape from the FDA’s labelling data. Match the imprint on your pill — or search any imprint.
Combination products containing letrozole
A combination is a different drug — different dosing, different warnings. It is listed here so you can find it, not so you can substitute it.
How long letrozole keeps
No letrozole label we read sets a separate limit for after opening, but they do specify how it must be stored — and the stability behind any date assumes those conditions.
Does letrozole expire? The in-use limits and storage rules from its labelsLetrozole and breastfeeding
From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.
Full LactMed record for letrozole: levels in milk, effects in breastfed infants, and the drugs it would consider insteadA minimal amount of information on letrozole excretion into milk indicates that the amounts might be of concern. Because of harm reported in animal studies, the manufacturer recommends that breastfeeding be discontinued during letrozole therapy and for 3 weeks after the last dose.
National Institute of Child Health and Human Development, record revised January 15, 2025. LactMed states its information is not a substitute for professional judgement.
What people report to the FDA about letrozole
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 49,117 reports naming letrozole, and the FDA flagged 80% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- fatigue6,127 reports
- neutropenia4,584 reports
- nausea4,478 reports
- diarrhoea3,916 reports
- malignant neoplasm progression3,740 reports
- white blood cell count decreased3,274 reports
- arthralgia3,053 reports
- alopecia2,869 reports
Read these as a signal, not a rate. A report does not mean letrozole caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.
Source: openFDA drug/event (FAERS), retrieved August 25, 2026.
How long letrozole stays in your system
The elimination half-life of letrozole is about 2 days (terminal elimination half-life). This is the terminal (elimination) half-life; the label states it directly and does not report a separate distribution phase. Letrozole is NOT a prodrug and has NO active metabolite that outlasts it — its main metabolite (the carbinol metabolite, 4,4'-methanol-bisbenzonitrile) is explicitly pharmacologically inactive, so there is no longer-lasting active moiety to report. Note that steady state on daily 2.5 mg dosing is not reached for 2 to 6 weeks. Population effects per the label: AGE — no change in pharmacokinetics was seen with increasing age (adults 35 to >80 years). KIDNEY — renal impairment (creatinine clearance down to ~9-20 mL/min) had no effect on letrozole pharmacokinetics or steady-state levels. LIVER — moderate hepatic impairment (Child-Pugh B) raised exposure (AUC) ~37% (still within the normal range), but severe impairment (Child-Pugh C, cirrhosis) roughly doubled exposure with a 47% drop in systemic clearance, so half-life/exposure is meaningfully prolonged in severe liver disease.
Letrozole tablet — DailyMed label, Section 12.3 Pharmacokinetics ↗Half-life is how long the body takes to clear half a dose. It is not the same as how long a drug test can detect it, and it varies with age, kidney and liver function.
Related calculators
Frequently asked questions
What is letrozole?
Femara (Letrozole) is an aromatase inhibitor used to treat Breast Neoplasms.
What kind of drug is letrozole?
The FDA classifies letrozole as an aromatase inhibitor. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.
How long does letrozole stay in your system?
The elimination half-life of letrozole is about 2 days (terminal elimination half-life) — that is how long the body takes to clear half of a dose. This is the terminal (elimination) half-life; the label states it directly and does not report a separate distribution phase. Letrozole is NOT a prodrug and has NO active metabolite that outlasts it — its main metabolite (the carbinol metabolite, 4,4'-methanol-bisbenzonitrile) is explicitly pharmacologically inactive, so there is no longer-lasting active moiety to report. Note that steady state on daily 2.5 mg dosing is not reached for 2 to 6 weeks. Population effects per the label: AGE — no change in pharmacokinetics was seen with increasing age (adults 35 to >80 years). KIDNEY — renal impairment (creatinine clearance down to ~9-20 mL/min) had no effect on letrozole pharmacokinetics or steady-state levels. LIVER — moderate hepatic impairment (Child-Pugh B) raised exposure (AUC) ~37% (still within the normal range), but severe impairment (Child-Pugh C, cirrhosis) roughly doubled exposure with a 47% drop in systemic clearance, so half-life/exposure is meaningfully prolonged in severe liver disease. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.
Can you take letrozole with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run letrozole against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What brand names is letrozole sold under?
We track 2 letrozole-containing products in the U.S.: Letrozole and Femara. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.
What forms does letrozole come in?
Across the brands we track, letrozole is currently marketed as tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic letrozole?
Yes. Our catalog lists 1 generic letrozole product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.
Cite this page
- APA
- pharmaranks. (2026, July 24). Letrozole: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/letrozole
- MLA
- “Letrozole: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/letrozole.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for letrozole on DailyMed (NIH) ↗.