letrozole
Brand names: Femara
Letrozole is a medicine that lowers estrogen levels in women after menopause. It is used to treat breast cancer that is affected by hormones.
Drug Pricing (NADAC)
Generic Price
$0.13/unit
Generic Available
Yes (6 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Letrozole is used to treat breast cancer in women who have gone through menopause.
Common side effects
Hot flashes, Joint pain, Flushing
Key warnings
Letrozole can cause bone thinning, which may lead to fractures.
How It Works
Letrozole blocks a protein called aromatase in the body. Aromatase makes estrogen. By blocking aromatase, letrozole lowers the amount of estrogen, which can slow or stop the growth of breast cancer cells that need estrogen to grow.
How to Take It
Take one 2.5 mg letrozole tablet once a day. You can take it with or without food. If you have liver problems, your doctor may have you take it every other day. Keep taking letrozole until your doctor tells you to stop.
Pregnancy & Breastfeeding
Do not take letrozole if you are pregnant because it can harm your unborn baby. If there is any chance you could become pregnant, use birth control while taking letrozole. Do not breastfeed while taking letrozole.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store letrozole tablets at room temperature, away from moisture and heat.
Side Effects (from patient reports)
Based on 42,900 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 59,013 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
59,013
Death-Related Reports
5,837
Hospitalization Reports
15,111
Top Indication
Breast Cancer
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | FATIGUE | 7,159 |
| 2 | NAUSEA | 5,259 |
| 3 | NEUTROPENIA | 4,896 |
| 4 | DIARRHOEA | 4,460 |
| 5 | MALIGNANT NEOPLASM PROGRESSION | 4,254 |
| 6 | ARTHRALGIA | 3,803 |
| 7 | WHITE BLOOD CELL COUNT DECREASED | 3,678 |
| 8 | ALOPECIA | 3,582 |
| 9 | PAIN | 2,959 |
| 10 | ASTHENIA | 2,852 |
| 11 | DYSPNOEA | 2,838 |
| 12 | NEOPLASM PROGRESSION | 2,802 |
| 13 | VOMITING | 2,679 |
| 14 | DEATH | 2,586 |
| 15 | HEADACHE | 2,388 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Letrozole can cause bone thinning, which may lead to fractures. Your doctor may monitor your bone density. Letrozole can also harm an unborn baby, so you must not take it if you are pregnant. Use effective birth control if you could become pregnant.
Known Drug Interactions
7 DRUG INTERACTIONS Anastrozole and letrozole: Should not be used in combination with tamoxifen. Letrozole The concomitant use of letrozole with tamoxifen is not recommended because the efficacy of the combination in the adjuvant treatment of breast cancer has not been established. Tamoxifen reduced the plasma concentration of letrozole by 38% when these drugs were co-administered [see Clinical Pharmacology (12.3) ].
Mechanism: Tamoxifen lowers the amount of letrozole in your blood, and it is not known if taking both together helps treat cancer effectively.
What to do: You should avoid using these two medications at the same time.
Warfarin An interaction study (P017) with warfarin showed no clinically significant effect of letrozole on warfarin pharmacokinetics.
Mechanism: Research shows that letrozole does not change how the body handles the blood thinner warfarin. There is no major interaction between these two drugs.
What to do: You can usually take these together without any changes, but keep following your doctor's plan for blood tests.
Cimetidine A pharmacokinetic interaction study with cimetidine (study P004) showed no clinically significant effect on letrozole pharmacokinetics.
Mechanism: Cimetidine does not have a significant effect on how letrozole moves through your body. The two drugs do not interfere with each other in a meaningful way.
What to do: No special precautions or dose changes are typically needed when taking these two medicines together.
7 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.
Mechanism: Cimetidine does not have a meaningful effect on how letrozole is processed or used by the body.
What to do: No special changes or dosage adjustments are needed when taking these two medications together.
Common Questions
Can I take letrozole if I am still having periods?
How long will I need to take letrozole?
Can letrozole cure my breast cancer?
Will letrozole cause me to gain weight?
Can I drink alcohol while taking letrozole?
What should I do if I experience severe side effects?
Does letrozole interact with other medications?
Will letrozole affect my cholesterol?
Can men take letrozole?
Is there a generic version of letrozole available?
What are the common side effects of letrozole?
Does letrozole interact with other medications?
What drug class is letrozole?
Is letrozole safe during pregnancy?
Related Medications in Aromatase Inhibitor
Other drugs grouped near letrozole — same-class peers and common alternatives.
abiraterone
Zytiga
Abiraterone (Zytiga) is a medicine used with prednisone to treat prostate cancer that has spread.
Compare with letrozole →
anastrozole
Arimidex
Anastrozole is a medicine used to treat breast cancer in women after menopause.
Compare with letrozole →
bazedoxifene/conjugated estrogens
Duavee
Duavee is a combination medicine containing estrogen and a drug that blocks estrogen in some parts of the body.
Compare with letrozole →
cabergoline
Dostinex
Cabergoline is a medicine that helps lower the amount of prolactin in your body.
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clomiphene
Clomid, Serophene
Clomiphene citrate is a medicine that helps women ovulate.
Compare with letrozole →
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What the FDA Data Shows for letrozole
The FDA label for letrozole (sold under brand names such as Femara) classifies it as a prescription-only medication in the Aromatase Inhibitor class. Letrozole is used to treat breast cancer in women who have gone through menopause. Official labeling lists 11 commonly reported side effects, including Hot flashes, Joint pain, Flushing.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 42,900 voluntary reports. The database also lists 4 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $0.13.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: August 24, 2023
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages