Prescription medication · Aromatase Inhibitor
letrozole
Also sold as Femara. Letrozole is used to treat breast cancer in women who have gone through menopause.
Data updated 2026-05-15
- 59,013
- FDA reportsOften reported
- 4
- InteractionsFew interactions
- $0.13
- Generic price (NADAC)
What the data shows
letrozole (Femara) is a prescription Aromatase Inhibitor, more reported than most tracked drugs (59,013 FDA reports), with 4 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
letrozole (Femara) is a prescription Aromatase Inhibitor. Letrozole is used to treat breast cancer in women who have gone through menopause.
Letrozole is a medicine that lowers estrogen levels in women after menopause. It is used to treat breast cancer that is affected by hormones.
Verify with FDA → · CMS NADAC pricing →
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 →
NADAC price trail: LETROZOLE 2.5 MG TABLET
Same CMS presentation as the headline generic unit price above (2 effective dates). Adjacent % compares consecutive NADAC releases for this description only, not a patient out-of-pocket quote. Latest step: +3.5% vs prior release.
| Effective | NADAC / unit | vs prior | NDCs |
|---|---|---|---|
| February 21, 2024 | $0.1295/EA | - | 1 |
| December 18, 2024 | $0.1340/EA | +3.5% | 14 |
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.
The sections below are summarized in plain English from letrozole's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
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.
Side Effects (from patient reports)
Based on 59,013 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for letrozole, by number of reports
- Fatigue
Fatigue
7,159 reports
- Nausea
Nausea
5,259 reports
- Neutropenia
Neutropenia
4,896 reports
- Diarrhoea
Diarrhoea
4,460 reports
- Malignant Neoplasm Progression
Malignant Neoplasm Progression
4,254 reports
- Arthralgia
Arthralgia
3,803 reports
- White Blood Cell Count Decreased
White Blood Cell Count Decreased
3,678 reports
- Alopecia
Alopecia
3,582 reports
- Pain
Pain
2,959 reports
- Asthenia 2,852
Asthenia
2,852 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for letrozole each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where letrozole sits
letrozole has more FDA adverse-event reports than 77% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is letrozole; the line is the median (50th percentile).
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
Reports Mentioning Death
5,837
9.9% of reports — not proof of cause
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) 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.
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.
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.
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.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
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?
What pregnancy or breastfeeding source fields are listed for letrozole?
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.
Compare with letrozole →
clomiphene
Clomid, Serophene
Clomiphene citrate is a medicine that helps women ovulate.
Compare with letrozole →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for letrozole: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 59,013.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 9.89%.
- benralizumab Δ 0.00 pts · 17,680 reports · Anti-IL-5R Monoclonal Antibody 9.89%death share
- famciclovir Δ 0.00 pts · 2,678 reports · Antiviral (Nucleoside Analog) 9.90%death share
- doxycycline hyclate Δ 0.01 pts · 63,762 reports · Tetracycline Antibiotic (Antimalarial) 9.90%death share
- dolutegravir Δ 0.01 pts · 8,756 reports · Integrase Strand Transfer Inhibitor 9.88%death share
Medication Guides
Understanding Drug Interactions
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Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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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 59,013 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 are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
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. This registry does not provide medication decisions.
Last updated: August 24, 2023
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
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