Aromatase Inhibitor side effects compared: 5 drugs, 188,163 FDA adverse event reports
Members
| Drug | FAERS reports | Serious | Death outcome | Boxed warning | Top labeled signals | Unlabeled (unassessed) |
|---|---|---|---|---|---|---|
| Letrozole | 61,227 | 81% | 6,035 | – | Hormone receptor positive her2 negative breast cancer | Neoplasm progression; Metastases to bone |
| Letrozole | 47,818 | 80% | 4,408 | – | Hormone receptor positive her2 negative breast cancer | Neoplasm progression; Metastases to bone |
| Anastrozole | 36,494 | 68% | 2,430 | – | Hair disorder; Trigger finger; Urinary tract disorder | Metastases to bone; Metastases to liver |
| Anastrozole | 21,328 | 74% | 1,543 | – | Hair disorder; Urinary tract disorder; Musculoskeletal toxicity | Metastases to bone; Metastases to lung |
| Exemestane | 21,296 | 77% | 2,512 | – | Metastases to bone; Metastases to liver; Urinary tract disorder | Breast cancer metastatic; Metastases to lymph nodes |
Class-wide signals (flagged in at least 3 of 5 members)
| Reaction | Members flagged | Median PRR | Reports (sum) | In label |
|---|---|---|---|---|
| Pik3ca-activated mutation | 5/5 | 337.1 | 530 | 0/5 members' labels |
| Amaurosis fugax | 5/5 | 152.4 | 1,138 | 0/5 members' labels |
| Pseudocirrhosis | 5/5 | 100.8 | 220 | 0/5 members' labels |
| Metastases to chest wall | 5/5 | 80.9 | 215 | 0/5 members' labels |
| Breast cancer metastatic | 5/5 | 78.3 | 5,475 | 0/5 members' labels |
| Metastases to thorax | 5/5 | 73.6 | 141 | 0/5 members' labels |
| Metastases to the mediastinum | 5/5 | 62.7 | 210 | 0/5 members' labels |
| Metastases to pleura | 5/5 | 61.2 | 465 | 0/5 members' labels |
| Breast cancer recurrent | 5/5 | 57.9 | 1,433 | 0/5 members' labels |
| Metastases to bone | 5/5 | 55.9 | 7,008 | 1/5 members' labels |
| Invasive lobular breast carcinoma | 5/5 | 53.2 | 215 | 0/5 members' labels |
| Metastases to pelvis | 5/5 | 48.2 | 262 | 0/5 members' labels |
| Metastases to spine | 5/5 | 43.2 | 1,120 | 1/5 members' labels |
| Hormone receptor positive breast cancer | 4/5 | 110.1 | 163 | 1/4 members' labels |
| Metastases to liver | 4/5 | 36.1 | 4,405 | 1/4 members' labels |
| Bone lesion | 4/5 | 32.9 | 859 | 1/4 members' labels |
| Hormone receptor positive her2 negative breast cancer | 3/5 | 328.4 | 303 | 3/3 members' labels |
| Pleural neoplasm | 3/5 | 105.5 | 70 | 0/3 members' labels |
| Metastases to skin | 3/5 | 65.4 | 418 | 1/3 members' labels |
| Bone marrow infiltration | 3/5 | 47.8 | 95 | 0/3 members' labels |
| Urinary tract disorder | 3/5 | 46.2 | 622 | 3/3 members' labels |
| Invasive breast carcinoma | 3/5 | 43.9 | 104 | 0/3 members' labels |
| Osteosclerosis | 3/5 | 38.9 | 285 | 0/3 members' labels |
| Metastases to bone marrow | 3/5 | 32.2 | 94 | 0/3 members' labels |
| Metastases to lymph nodes | 3/5 | 31.5 | 1,284 | 0/3 members' labels |
| Primary sequestrum | 3/5 | 30.3 | 168 | 0/3 members' labels |
| Metastases to lung | 3/5 | 29.9 | 1,760 | 0/3 members' labels |
Member-specific signals (flagged in exactly one drug)
| Reaction | Drug | Reports | PRR | Label screen |
|---|---|---|---|---|
| Trigger finger | Anastrozole | 247 | 37.2 | Labeled adverse reaction |
| Vulvovaginal dryness | Anastrozole | 171 | 32.2 | Not in label — unassessed |
| Haemorrhagic stroke | Anastrozole | 242 | 31.2 | Not in label — unassessed |
| Anisocytosis | Letrozole | 53 | 30.4 | Not in label — unassessed |
| Madarosis | Anastrozole | 552 | 28.4 | Not in label — unassessed |
| Hair colour changes | Anastrozole | 591 | 28.3 | Not in label — unassessed |
| Hair texture abnormal | Anastrozole | 630 | 28.1 | Not in label — unassessed |
| Psychological trauma | Anastrozole | 400 | 27.5 | Not in label — unassessed |
Common questions
Which aromatase inhibitor has the most FDA adverse event reports?
Letrozole has the most FAERS co-reports in this class (61,227), followed by Letrozole (47,818). Report volume tracks how widely and how long a drug has been used, and how much attention it has had, far more than its risk.
Which side effects are shared across aromatase inhibitor drugs?
Reaction terms flagged in at least half of the 5 members include pik3ca-activated mutation, amaurosis fugax, pseudocirrhosis, metastases to chest wall, breast cancer metastatic. A term shared across a class usually reflects the shared mechanism (or the shared patient population) rather than one product.
Does a FAERS signal mean the drug causes the reaction?
No. These are disproportionality signals from voluntary reports with no denominator. Each is screened against the FDA label (known vs unlabeled) on the drug pages; causality needs temporality, dose-response, plausibility and trial or cohort evidence.
Sources: openFDA FAERS pair statistics (OpenPV build 2026-09-14), FDA labels via openFDA, seriousness and death counts from openFDA count queries. Generated 2026-10-08. Not medical advice.