What the label lists and what reports show
Letrozole side effects
Letrozole's FDA label: “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.” FAERS holds 61,238 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (7,411 reports).
- Generic listed
Check it at the source: the letrozole FDA label on DailyMed (effective June 11, 2026, Novartis Pharmaceuticals Corporation); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (greater than 20%) were hot flashes, arthralgia; flushing, asthenia, edema, arthralgia, headache, dizziness, hypercholesterolemia, sweating increased, bone pain; and musculoskeletal.
Table 3: Adverse Reactions Occurring in at Least 5% of Patients in Either Treatment Arm
| Reaction | Femara N = 2563 | Placebo N = 2573 | Femara N = 2563 | Placebo N = 2573 |
|---|---|---|---|---|
| Any Adverse Reaction s | 2232 (87.1) | 2174 (84.5) | 419 (16.3) | 389 (15.1) |
| Vascular Disorders | 1375 (53.6) | 1230 (47.8) | 59 (2.3) | 74 (2.9) |
| Flushing | 1273 (49.7) | 1114 (43.3) | 3 (0.1) | 0 |
| General Disorders | 1154 (45) | 1090 (42.4) | 30 (1.2) | 28 (1.1) |
| Asthenia | 862 (33.6) | 826 (32.1) | 16 (0.6) | 7 (0.3) |
| Edema NOS | 471 (18.4) | 416 (16.2) | 4 (0.2) | 3 (0.1) |
| Musculoskeletal Disorders | 978 (38.2) | 836 (32.5) | 71 (2.8) | 50 (1.9) |
| Arthralgia | 565 (22) | 465 (18.1) | 25 (1) | 20 (0.8) |
| Arthritis NOS | 173 (6.7) | 124 (4.8) | 10 (0.4) | 5 (0.2) |
| Myalgia | 171 (6.7) | 122 (4.7) | 8 (0.3) | 6 (0.2) |
| Back Pain | 129 (5) | 112 (4.4) | 8 (0.3) | 7 (0.3) |
| Nervous System Disorders | 863 (33.7) | 819 (31.8) | 65 (2.5) | 58 (2.3) |
| Headache | 516 (20.1) | 508 (19.7) | 18 (0.7) | 17 (0.7) |
| Dizziness | 363 (14.2) | 342 (13.3) | 9 (0.4) | 6 (0.2) |
| Skin Disorders | 830 (32.4) | 787 (30.6) | 17 (0.7) | 16 (0.6) |
| Sweating Increased | 619 (24.2) | 577 (22.4) | 1 (< 0.1) | 0 |
| Gastrointestinal Disorders | 725 (28.3) | 731 (28.4) | 43 (1.7) | 42 (1.6) |
| Constipation | 290 (11.3) | 304 (11.8) | 6 (0.2) | 2 (< 0.1) |
| Nausea | 221 (8.6) | 212 (8.2) | 3 (0.1) | 10 (0.4) |
| Diarrhea NOS | 128 (5) | 143 (5.6) | 12 (0.5) | 8 (0.3) |
| Metabolic Disorders | 551 (21.5) | 537 (20.9) | 24 (0.9) | 32 (1.2) |
| Hypercholesterolemia | 401 (15.6) | 398 (15.5) | 2 (< 0.1) | 5 (0.2) |
| Reproductive Disorders | 303 (11.8) | 357 (13.9) | 9 (0.4) | 8 (0.3) |
| Vaginal Hemorrhage | 123 (4.8) | 171 (6.6) | 2 (< 0.1) | 5 (0.2) |
| Vulvovaginal Dryness | 137 (5.3) | 127 (4.9) | 0 | 0 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe 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. …
Source: FDA drug label, Novartis Pharmaceuticals Corporation, effective June 11, 2026 (SPL set 82b77d74-085f-45ac-a7dd-1f5c038bf406), via openFDA; the full label on DailyMed
What do FAERS reports show?
61,238 reports list letrozole among the medicines taken, each a report of something that happened, not proof the medicine caused it; 6,036 are coded as a death and 15,648 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 22 reactions below, 13 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Letrozole: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions