Brand name · Letrozole
Femara: adverse event reports filed with FDA
8,770 reports list it as a suspect or interacting product, 2004–2026. Class: Aromatase inhibitor.
- 8,770
- reports as suspect product
- 0% of all reports · about 390 a year
- 367
- reports, 12 months to June 2026
- 397 in the 12 months before
- 89.1%
- marked serious by the reporter
- 82.2% across the class
- 13.1%
- record death among outcomes, as reported
- 1,153 reports · not verified by FDA
Between January 2004 and June 2026, 8,770 adverse event reports received by FDA list the brand name Femara (letrozole) as a suspect or interacting product. Reports that mention it only as a concomitant medication (5,324) are left out of every figure here.
In the 12 months to June 2026, 367 reports listed it, close to the 397 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 390 reports a year and 0% of the 20,646,523 reports in the database, and 12.5% of the reports for the aromatase inhibitor class. How many people take it is not in the data, so a count is not a rate of occurrence.
The reactions recorded most often are fatigue (10%), arthralgia (8.5%) and malignant neoplasm progression (8.4%). A report can list several reactions, so shares add to more than 100%; 1,432 different terms appear across these reports. Fatigue is recorded in 10% of these reports, about the same share as in the median aromatase inhibitor drug (10.6%).
89.1% of the reports are marked serious by the reporter (82.2% across the class); 13.1% record death among the outcomes and 26.3% record hospitalisation, as reported. 41% of the reports came from consumers, and the largest patient age group is 45 to 64 (22.5%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
Reports by month, five years
Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.
By year received
2026 covers reports received through June 2026 only.
Reactions recorded in the reports
share of Femara reports recording the termmedian drug in aromatase inhibitor
- Fatiguetiredness10%880
- Arthralgiajoint pain8.5%743
- Nauseafeeling sick7.8%687
- Deaththe patient died; cause not stated by this term6.6%582
- Painpain, site not specified5.5%486
- Diarrhoealoose or frequent stools5.4%477
- Astheniaweakness or lack of energy5%439
- Breast cancerbreast cancer4.7%413
- Alopeciahair loss4.7%412
- Headachehead pain4.7%412
- Vomitingbeing sick4.7%410
- Neutropenialow neutrophils, a type of white blood cell4.5%399
- Malaisegeneral feeling of being unwell4.4%388
- Pain in extremitypain in an arm or leg4.1%363
- Metastases to bone4.1%362
- Bone painbone pain4.1%361
- Dyspnoeashortness of breath4%350
- Dizzinesslight-headedness or unsteadiness3.7%325
- Decreased appetitereduced appetite3.5%310
- Pyrexiafever3.5%309
- Hot flusha hot flush3.5%303
- White blood cell count decreasedlow white cell count3.4%299
- Back painback pain3.2%285
- Insomniadifficulty sleeping3.1%268
- Myalgiamuscle pain3%267
- Anaemialow red blood cells3%261
- Weight decreasedweight loss2.9%251
- Coughcough2.9%250
- Falla fall2.9%250
Top 30 of 1,432 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 6 drugs in the aromatase inhibitor class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Outcomes recorded
Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 70,406 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."
Patients and reporters
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 38.2% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Breast cancer | 3,337 | 38.1% |
| Breast cancer metastatic | 868 | 9.9% |
| Her2 positive breast cancer | 184 | 2.1% |
| Breast cancer female | 152 | 1.7% |
| Neoplasm malignant | 109 | 1.2% |
| Hormone receptor positive her2 negative breast cancer | 97 | 1.1% |
The indication field is filled in by the reporter and is often blank; shares are of all 8,770 reports.
Drugs most often listed in the same reports
| Drug (any role in the report) | Reports | Share of Femara reports |
|---|---|---|
| Kisqali | 1,341 | 15.3% |
| Ibrance | 702 | 8% |
| Aromasin | 398 | 4.5% |
| Palbociclib | 392 | 4.5% |
| Zometa | 382 | 4.4% |
| Xgeva | 378 | 4.3% |
| Faslodex | 330 | 3.8% |
| Herceptin | 305 | 3.5% |
| Letrozole | 294 | 3.4% |
| Tamoxifen | 287 | 3.3% |
Other products listed in reports where Femara is a suspect product, whatever their own role. Co-listing means the two were recorded together; it says nothing about either product's part in the event. Only the 2,500 most-reported names are counted here.
In context
| Measure | Femara | Aromatase inhibitor | All reports |
|---|---|---|---|
| Reports as suspect product | 8,770 | 70,406 | 20,646,523 |
| Share of that pool | — | 12.5% | 0% |
| Reports, latest 12 months | 367 | — | 1,332,454 |
| Marked serious | 89.1% | 82.2% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 131 | 94 | 91 |
| Hospitalisation recorded, per 1,000 reports | 263 | 240 | 213 |
| Consumer-filed share | 41% | 31.6% | 45.8% |
| Top term, share of reports | Fatigue 10% | median 10.6% | 3.7% |
Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Other drugs in the aromatase inhibitor class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Letrozole | generic | 27,849 | 2,523 | 89.9% |
| Arimidex | brand | 10,217 | 95 | 58% |
| Anastrozole | generic | 10,122 | 1,234 | 86.4% |
| Exemestane | generic | 7,041 | 473 | 85.5% |
| Aromasin | brand | 6,407 | 112 | 67.6% |
Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.
Questions about Femara reports
How many adverse event reports has FDA received for Femara?
8,770 reports list Femara as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 367 of them arrived in the latest 12 months. Another 5,324 list it only as a concomitant medication.
What reactions are recorded in Femara reports?
fatigue (10%), arthralgia (8.5%), malignant neoplasm progression (8.4%), nausea (7.8%) and death (6.6%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Femara was responsible.
How serious are the reports?
89.1% are marked serious by the reporter. Among the outcomes recorded, 13.1% of reports include death and 26.3% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
consumer or non-health professional (41%), physician (30.1%) and other health professional (14.3%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Femara rising?
367 reports in the 12 months to June 2026, close to the 397 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Femara was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Femara?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. See the guide on how to report.
Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Femara as a suspect or interacting product; reports listing it only as a concomitant medication (5,324) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.
Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.