Drug · FAERS side-effect profile with label screen
Letrozole side effects: what 61,227 FDA adverse event reports show
Who reports
61,227 reports · 81% serious · 6,035 with death outcome · 98% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Letrozole tablets are an aromatase inhibitor indicated for: Adjuvant treatment of postmenopausal women with hormone receptor positive early breast cancer (1.1) Extended adjuvant treatment of postmenopausal women with early breast cancer who have receiv.
FDA label, Indications and Usage
What it is
Letrozole Tablets USP for oral administration contain 2.5 mg of letrozole, USP, a nonsteroidal aromatase inhibitor (inhibitor of estrogen synthesis). It is chemically described as 4,4'-(1 H -1,2,4triazol-1-ylmethylene)dibenzonitrile, and its structural formula is: C 17 H 11 N 5 M.W.
FDA label, Description section
Boxed warning
None in the current label
How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation.
Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)?
That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.
Causality screen of the 40 strongest signals
Labeled (related wording) 1Likely indication confounding 2Lab value / disease marker 9Not in label — unassessed 28
What the badges mean
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
- Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
- Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.
Strongest disproportionality signals
Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only (and, for the 300 most-reported drugs, adjusted for age band), and flags pairs whose reports are unusually skewed by sex or come mostly from consumers. Each row also shows the PRR against the other drugs of the same FDA class, which removes most confounding by the condition being treated, and a calibrated p-value: on validation, known non-causes average an ROR of about 2, so significance is judged against that empirical null (✓ = p < 0.05 after calibration). 1,211 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
Show:
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Pik3ca-activated mutation | 182 | 438.0 351.5–545.9ROR 439.3 · calibrated p 4e-13 ✓ | 187.3 EB05 165.5 · IC025 +6.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (1.7–2.5) | Not in label — unassessed | serious n=182 | not reported in cached trials |
| Hormone receptor positive her2 negative breast cancer | 153 | 328.4 262.8–410.2ROR 329.2 · calibrated p 7e-12 ✓ | 163.4 EB05 142.8 · IC025 +6.5 3/3 methods agree vs other Aromatase Inhibitors: PRR 4.1 (3.3–5.1) | Labeled (related wording) related wording | serious n=153 | not reported in cached trials |
| Carbohydrate antigen 15-3 increased | 302 | 226.1 195.5–261.6ROR 227.2 · calibrated p 2e-10 ✓ | 134.6 EB05 122.3 · IC025 +6.6 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.4 (2.1–2.8) | Lab value / disease marker | serious n=294 | not reported in cached trials |
| Carbohydrate antigen 27.29 increased | 42 | 132.3 92.6–189.0ROR 132.3 · calibrated p 3e-8 ✓ | 91.4 EB05 70.5 · IC025 +5.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 3.9 (2.6–6.0) | Lab value / disease marker | serious n=36 · 100% consumer | not reported in cached trials |
| Hormone receptor positive breast cancer | 59 | 98.9 74.0–132.2ROR 99.0 · calibrated p 2e-7 ✓ | 74.9 EB05 60.2 · IC025 +5.1 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.3 (1.6–3.1) | Likely indication confounding term in indications; also in warnings | serious n=59 · 100% clinician | not reported in cached trials |
| Amaurosis fugax | 233 | 95.4 82.5–110.3ROR 95.8 · calibrated p 2e-7 ✓ | 74.1 EB05 66.5 · IC025 +5.8 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.0 (0.9–1.2) | Not in label — unassessed | serious n=233 · 93% clinician | not reported in cached trials |
| Breast cancer metastatic | 1,997 | 78.3 74.6–82.2ROR 80.9 · calibrated p 5e-7 ✓ | 63.7 EB05 61.4 · IC025 +5.9 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.3 (2.2–2.4) | Likely indication confounding term in indications; also in warnings | serious PRR 45.1 | not reported in cached trials |
| Metastases to chest wall | 63 | 76.1 57.9–100.0ROR 76.2 · calibrated p 1e-6 ✓ | 61.2 EB05 49.5 · IC025 +5.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.7 (1.2–2.2) | Not in label — unassessed | serious n=63 | not reported in cached trials |
| Metastases to thorax | 45 | 73.6 53.3–101.6ROR 73.7 · calibrated p 2e-6 ✓ | 59.1 EB05 46.0 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.9 (1.3–2.7) | Not in label — unassessed | serious n=45 | not reported in cached trials |
| Tumour marker abnormal | 57 | 70.1 52.7–93.2ROR 70.2 · calibrated p 2e-6 ✓ | 57.1 EB05 45.7 · IC025 +4.8 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.5 (1.8–3.4) | Lab value / disease marker | serious n=46 · 100% consumer | not reported in cached trials |
| Metastases to skin | 161 | 63.8 53.9–75.5ROR 64.0 · calibrated p 3e-6 ✓ | 53.5 EB05 46.9 · IC025 +5.3 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (1.7–2.5) | Not in label — unassessed | serious n=161 | not reported in cached trials |
| Metastases to pleura | 158 | 61.2 51.7–72.5ROR 61.3 · calibrated p 4e-6 ✓ | 51.6 EB05 45.2 · IC025 +5.2 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (1.7–2.5) | Not in label — unassessed | serious n=158 | not reported in cached trials |
| Metastases to the mediastinum | 63 | 61.2 46.8–80.0ROR 61.2 · calibrated p 5e-6 ✓ | 51.2 EB05 41.4 · IC025 +4.8 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.7 (1.3–2.3) | Not in label — unassessed | serious n=63 · 100% clinician | not reported in cached trials |
| Metastases to bone | 2,367 | 57.9 55.5–60.4ROR 60.2 · calibrated p 4e-6 ✓ | 49.5 EB05 47.9 · IC025 +5.5 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (1.9–2.1) | Not in label — unassessed | serious PRR 35.6 | not reported in cached trials |
| Pseudocirrhosis | 47 | 57.2 42.0–77.9ROR 57.2 · calibrated p 9e-6 ✓ | 48.1 EB05 37.6 · IC025 +4.5 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.1 (0.8–1.5) | Not in label — unassessed | serious n=47 · 100% clinician | not reported in cached trials |
| Breast cancer recurrent | 429 | 53.9 48.7–59.7ROR 54.3 · calibrated p 8e-6 ✓ | 46.5 EB05 42.9 · IC025 +5.3 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.7 (1.5–1.9) | Not in label — unassessed | serious n=424 | not reported in cached trials |
| Invasive lobular breast carcinoma | 69 | 53.2 41.3–68.6ROR 53.3 · calibrated p 1e-5 ✓ | 45.5 EB05 37.2 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.9 (1.4–2.5) | Not in label — unassessed | serious n=66 | not reported in cached trials |
| Metastases to pelvis | 78 | 48.2 38.0–61.1ROR 48.3 · calibrated p 2e-5 ✓ | 41.9 EB05 34.7 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.7 (1.3–2.2) | Not in label — unassessed | serious n=78 | not reported in cached trials |
| Tumour marker increased | 565 | 45.5 41.7–49.7ROR 45.9 · calibrated p 2e-5 ✓ | 40.2 EB05 37.5 · IC025 +5.1 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (1.9–2.3) | Lab value / disease marker | serious n=481 | not reported in cached trials |
| Invasive breast carcinoma | 47 | 43.9 32.4–59.4ROR 43.9 · calibrated p 4e-5 ✓ | 38.4 EB05 30.0 · IC025 +4.3 3/3 methods agree vs other Aromatase Inhibitors: PRR 3.3 (2.2–4.9) | Not in label — unassessed | serious n=47 · 100% clinician | not reported in cached trials |
| Metastases to spine | 376 | 43.2 38.8–48.1ROR 43.5 · calibrated p 3e-5 ✓ | 38.3 EB05 35.2 · IC025 +5.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (1.8–2.3) | Not in label — unassessed | serious n=376 | not reported in cached trials |
| Metastases to stomach | 40 | 39.6 28.6–55.0ROR 39.7 · calibrated p 8e-5 ✓ | 35.0 EB05 26.8 · IC025 +4.1 3/3 methods agree vs other Aromatase Inhibitors: PRR 5.2 (3.2–8.2) | Not in label — unassessed | serious n=40 · 100% consumer | not reported in cached trials |
| Osteosclerosis | 163 | 39.4 33.5–46.3ROR 39.5 · calibrated p 6e-5 ✓ | 35.2 EB05 30.9 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.7 (2.2–3.2) | Not in label — unassessed | serious n=160 | not reported in cached trials |
| Bone marrow infiltration | 38 | 37.3 26.7–52.2ROR 37.4 · calibrated p 1e-4 ✓ | 33.2 EB05 25.2 · IC025 +4.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.7 (1.8–4.0) | Not in label — unassessed | serious n=38 · 100% clinician | not reported in cached trials |
| Neutrophil percentage decreased | 52 | 37.0 27.8–49.3ROR 37.1 · calibrated p 1e-4 ✓ | 33.1 EB05 26.2 · IC025 +4.2 3/3 methods agree vs other Aromatase Inhibitors: PRR 4.4 (3.0–6.6) | Lab value / disease marker | serious n=50 · 100% consumer | not reported in cached trials |
| Metastases to liver | 1,674 | 36.1 34.3–37.9ROR 37.1 · calibrated p 8e-5 ✓ | 32.7 EB05 31.4 · IC025 +4.9 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (2.0–2.2) | Not in label — unassessed | serious PRR 23.4 | not reported in cached trials |
| Bone lesion | 341 | 35.7 31.9–39.9ROR 35.9 · calibrated p 1e-4 ✓ | 32.3 EB05 29.5 · IC025 +4.8 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.3 (2.0–2.6) | Not in label — unassessed | serious n=334 | not reported in cached trials |
| Lymphocyte percentage increased | 37 | 34.3 24.5–48.2ROR 34.4 · calibrated p 2e-4 ✓ | 30.8 EB05 23.3 · IC025 +3.9 3/3 methods agree vs other Aromatase Inhibitors: PRR 4.6 (2.9–7.4) | Lab value / disease marker | serious n=35 · 100% consumer | not reported in cached trials |
| Carcinoembryonic antigen increased | 171 | 33.2 28.4–38.8ROR 33.3 · calibrated p 2e-4 ✓ | 30.2 EB05 26.6 · IC025 +4.6 3/3 methods agree vs other Aromatase Inhibitors: PRR 3.1 (2.6–3.8) | Lab value / disease marker | serious n=171 | not reported in cached trials |
| Invasive ductal breast carcinoma | 241 | 33.2 29.1–37.9ROR 33.3 · calibrated p 2e-4 ✓ | 30.2 EB05 27.2 · IC025 +4.6 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (1.8–2.5) | Not in label — unassessed | serious n=241 | not reported in cached trials |
| Metastases to bone marrow | 44 | 32.7 24.0–44.6ROR 32.7 · calibrated p 2e-4 ✓ | 29.6 EB05 22.9 · IC025 +4.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 3.5 (2.3–5.3) | Not in label — unassessed | serious n=43 | not reported in cached trials |
| Metastases to lymph nodes | 566 | 31.5 28.9–34.3ROR 31.8 · calibrated p 2e-4 ✓ | 28.9 EB05 26.9 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (1.8–2.2) | Not in label — unassessed | serious n=564 | not reported in cached trials |
| Breast conserving surgery | 42 | 30.6 22.3–41.9ROR 30.6 · calibrated p 3e-4 ✓ | 27.8 EB05 21.4 · IC025 +3.9 3/3 methods agree vs other Aromatase Inhibitors: PRR 4.4 (2.9–6.9) | Not in label — unassessed | serious n=42 · 100% consumer | not reported in cached trials |
| Anisocytosis | 53 | 30.4 22.9–40.2ROR 30.4 · calibrated p 3e-4 ✓ | 27.7 EB05 22.0 · IC025 +4.0 3/3 methods agree vs other Aromatase Inhibitors: PRR 5.7 (3.8–8.7) | Not in label — unassessed | serious n=51 | not reported in cached trials |
| Metastases to lung | 929 | 29.9 28.0–32.0ROR 30.4 · calibrated p 2e-4 ✓ | 27.5 EB05 26.1 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.9 (1.8–2.1) | Not in label — unassessed | serious PRR 19.8 | not reported in cached trials |
| Neoplasm progression | 2,793 | 29.5 28.4–30.7ROR 30.9 · calibrated p 2e-4 ✓ | 27.2 EB05 26.4 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.6 (2.5–2.8) | Not in label — unassessed | age-adj. PRR 26.1 · serious PRR 19.7 | not reported in cached trials |
| Primary sequestrum | 73 | 29.5 23.2–37.5ROR 29.6 · calibrated p 3e-4 ✓ | 27.1 EB05 22.2 · IC025 +4.1 3/3 methods agree vs other Aromatase Inhibitors: PRR 3.1 (2.3–4.2) | Not in label — unassessed | serious n=73 | not reported in cached trials |
| Mean cell haemoglobin increased | 131 | 29.3 24.5–35.0ROR 29.3 · calibrated p 3e-4 ✓ | 26.9 EB05 23.3 · IC025 +4.3 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.7 (2.2–3.4) | Lab value / disease marker | serious n=117 | not reported in cached trials |
| Metastases to peritoneum | 191 | 28.2 24.3–32.7ROR 28.3 · calibrated p 4e-4 ✓ | 26.1 EB05 23.1 · IC025 +4.4 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.8 (2.3–3.3) | Not in label — unassessed | serious n=191 | not reported in cached trials |
| Basophil count increased | 51 | 24.8 18.7–33.0ROR 24.9 · calibrated p 9e-4 ✓ | 23.0 EB05 18.2 · IC025 +3.8 3/3 methods agree vs other Aromatase Inhibitors: PRR 4.9 (3.2–7.3) | Lab value / disease marker | serious n=44 | not reported in cached trials |
Clinical concept groups
MedDRA splits one clinical problem across several terms (e.g. "neutropenia", "neutrophil count decreased", "agranulocytosis"), which dilutes term-level signals. These rows count reports with any term in a concept group (an exact union, not a sum), compared with all other drugs. Groups are hand-built and listed in the methods.
| Concept | Reports | PRR 95% CI | Reading |
|---|---|---|---|
| Neutropenia / agranulocytosis | 6,613 | 9.49.2–9.6 | signal |
| Osteonecrosis | 1,247 | 7.57.1–8.0 | signal |
| Thrombocytopenia | 2,520 | 4.03.8–4.1 | signal |
| Anaemia | 3,365 | 3.93.7–4.0 | signal |
| Interstitial lung disease | 1,071 | 3.93.6–4.1 | signal |
| Liver injury | 2,792 | 3.23.1–3.3 | signal |
| Arrhythmia / qt | 1,341 | 2.42.3–2.5 | signal |
| Malignancy | 2,433 | 2.22.1–2.3 | signal |
| Venous thromboembolism | 1,372 | 2.22.1–2.3 | signal |
| Tendon disorder | 236 | 2.11.9–2.4 | raised |
| Depression | 1,427 | 1.71.7–1.8 | raised |
| Kidney injury | 2,264 | 1.71.6–1.8 | raised |
| Fall / fracture | 1,807 | 1.61.6–1.7 | raised |
| Hyponatraemia | 380 | 1.61.5–1.8 | raised |
| Serious infection | 3,596 | 1.61.5–1.6 | raised |
| Heart failure | 810 | 1.61.5–1.7 | raised |
Trial evidence (ClinicalTrials.gov)
✓ Trial adverse-event data found on ClinicalTrials.gov
Largest completed trials with posted results that list Letrozole as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (0 of 40 signal terms matched).
- NCT01272037 — Tamoxifen Citrate, Letrozole, Anastrozole, or Exemestane With or Without Chemotherapy in Treating Patients Wit (N=5018, PHASE3; 16 AE terms posted; arms: Chemo and Endocrine Therapy; Endocrine Therapy Alone)
- NCT00553410 — Letrozole in Preventing Cancer in Postmenopausal Women Who Have Received 4-6 Years of Hormone Therapy for Horm (N=4884, PHASE3; 225 AE terms posted; arms: Arm A: Continuous Letrozole; Arm B: Intermittent Letrozole)
Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.
Most frequently reported reactions
By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Fatigue (tiredness) | 7,410 | 3.3 3.2–3.4ROR 3.6 · calibrated p 0.460 | 3.3 EB05 3.2 · IC025 +1.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.1 (2.0–2.2) | Labeled adverse reaction exact term | age-adj. PRR 3.0 · serious PRR 3.1 | NCT00553410: 48/2,417 (2.0%) on Letrozole (serious AE) |
| Nausea | 5,486 | 2.4 2.3–2.5ROR 2.5 · calibrated p 0.801 | 2.4 EB05 2.3 · IC025 +1.2 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (2.0–2.1) | Labeled adverse reaction exact term | age-adj. PRR 2.1 · serious PRR 2.5 | NCT00553410: 2/2,417 (0.1%) on Letrozole (serious AE) |
| Neutropenia (low neutrophils (infection-fighting cells)) | 5,159 | 13.5 13.2–13.9ROR 14.7 · calibrated p 0.008 ✓ | 13.0 EB05 12.7 · IC025 +3.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.9 (2.9–3.0) | Not in label — unassessed | age-adj. PRR 10.9 · serious PRR 9.5 | NCT00553410: 1/2,417 (0.0%) on Letrozole (serious AE) |
| Diarrhoea (diarrhea) | 4,668 | 2.5 2.4–2.6ROR 2.6 · calibrated p 0.764 | 2.5 EB05 2.4 · IC025 +1.3 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.9 (1.9–2.0) | Labeled adverse reaction exact term | age-adj. PRR 2.1 · serious PRR 2.4 | NCT00553410: 5/2,417 (0.2%) on Letrozole (serious AE) |
| Malignant neoplasm progression | 4,499 | 15.8 15.3–16.2ROR 17.0 · calibrated p 0.004 ✓ | 15.1 EB05 14.8 · IC025 +3.9 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.3 (2.2–2.4) | Reporting / coding artifact | age-adj. PRR 11.2 · serious PRR 11.0 | not reported in cached trials |
| Arthralgia (joint pain) | 3,957 | 3.3 3.2–3.4ROR 3.5 · calibrated p 0.497 | 3.3 EB05 3.2 · IC025 +1.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.7 (1.6–1.7) | Labeled adverse reaction exact term | age-adj. PRR 2.6 · serious PRR 3.4 | not reported in cached trials |
| White blood cell count decreased | 3,800 | 12.4 12.0–12.8ROR 13.2 · calibrated p 0.012 ✓ | 12.0 EB05 11.7 · IC025 +3.5 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.7 (2.6–2.8) | Labeled (related wording) related wording | age-adj. PRR 12.0 · serious PRR 8.1 | not reported in cached trials |
| Alopecia (hair loss) | 3,672 | 6.5 6.3–6.7ROR 6.8 · calibrated p 0.105 | 6.4 EB05 6.2 · IC025 +2.6 3/3 methods agree vs other Aromatase Inhibitors: PRR 1.9 (1.8–2.0) | Labeled adverse reaction exact term | age-adj. PRR 7.2 · serious PRR 6.2 | not reported in cached trials |
| Pain | 3,046 | 1.7 1.6–1.8ROR 1.7 · calibrated p 0.791 | 1.7 EB05 1.6 · IC025 +0.7 vs other Aromatase Inhibitors: PRR 2.0 (1.9–2.0) | Labeled adverse reaction exact term | age-adj. PRR 1.8 · serious PRR 1.6 | NCT00553410: 1/2,411 (0.0%) on Letrozole (serious AE) |
| Asthenia (weakness) | 2,977 | 2.7 2.6–2.8ROR 2.8 · calibrated p 0.690 | 2.7 EB05 2.6 · IC025 +1.4 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.0 (1.9–2.0) | Labeled adverse reaction exact term | age-adj. PRR 2.2 · serious PRR 2.4 | NCT00553410: 48/2,417 (2.0%) on Letrozole (serious AE) |
| Dyspnoea (shortness of breath) | 2,935 | 1.8 1.7–1.8ROR 1.8 · calibrated p 0.842 | 1.8 EB05 1.7 · IC025 +0.8 vs other Aromatase Inhibitors: PRR 1.8 (1.8–1.9) | Labeled adverse reaction exact term | age-adj. PRR 1.4 · serious PRR 1.6 | NCT00553410: 5/2,417 (0.2%) on Letrozole (serious AE) |
| Neoplasm progression | 2,793 | 29.5 28.4–30.7ROR 30.9 · calibrated p 2e-4 ✓ | 27.2 EB05 26.4 · IC025 +4.7 3/3 methods agree vs other Aromatase Inhibitors: PRR 2.6 (2.5–2.8) | Not in label — unassessed | age-adj. PRR 26.1 · serious PRR 19.7 | not reported in cached trials |
| Vomiting | 2,776 | 2.0 2.0–2.1ROR 2.1 · calibrated p 0.989 | 2.0 EB05 2.0 · IC025 +1.0 vs other Aromatase Inhibitors: PRR 2.0 (1.9–2.1) | Labeled adverse reaction exact term | age-adj. PRR 1.8 · serious PRR 1.9 | NCT00553410: 1/2,417 (0.0%) on Letrozole (serious AE) |
| Death | 2,682 | 1.1 1.0–1.1ROR 1.1 · calibrated p 0.352 | 1.1 EB05 1.0 · IC025 +0.0 vs other Aromatase Inhibitors: PRR 2.5 (2.4–2.6) | Outcome field, not a reaction | age-adj. PRR 1.1 · serious PRR 0.8 | NCT01272037: 1/2,062 (0.0%) on Letrozole (serious AE) |
| Headache | 2,477 | 1.4 1.3–1.4ROR 1.4 · calibrated p 0.556 | 1.4 EB05 1.3 · IC025 +0.4 vs other Aromatase Inhibitors: PRR 1.7 (1.6–1.7) | Labeled adverse reaction exact term | age-adj. PRR 1.2 · serious PRR 1.6 | NCT00553410: 5/2,417 (0.2%) on Letrozole (serious AE) |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Pik3ca-activated mutation — n=182, PRR 438.0
- Amaurosis fugax — n=233, PRR 95.4
- Metastases to chest wall — n=63, PRR 76.1
- Metastases to thorax — n=45, PRR 73.6
- Metastases to skin — n=161, PRR 63.8
- Metastases to pleura — n=158, PRR 61.2
- Metastases to the mediastinum — n=63, PRR 61.2
- Metastases to bone — n=2,367, PRR 57.9
- Pseudocirrhosis — n=47, PRR 57.2
- Breast cancer recurrent — n=429, PRR 53.9
Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.
Common questions
What are the most reported side effects of Letrozole?
In FDA FAERS, the most frequently co-reported reaction terms for Letrozole are fatigue, nausea, neutropenia, diarrhoea, arthralgia, white blood cell count decreased. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.
Does Letrozole have an FDA boxed warning?
No. The FDA label retrieved for Letrozole has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Letrozole causes these side effects?
No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.
Sources & methods
- FDA label via openFDA (set ID 1524730f-e37d-478c-1956-b113b3ca42a8, effective 20251119; matched on
openfda.generic_name.exact:"LETROZOLE") - Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
- FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA
count=aggregation, fieldpatient.drug.openfda.generic_name.exact, 1,251 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction - Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
- Seriousness and sex counts from openFDA
count=serious,patient.patientsex,seriousnessdeath - ClinicalTrials.gov API v2 (query
LETROZOLE, results-bearing studies sorted by enrollment)
Page generated 2026-10-14. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.