Fulvestrant side effects: what 32,837 FDA adverse event reports show

Fulvestrant · 1,194 reaction terms · 156,174 drug–reaction co-reports · data 2026-09-14

Drug class

Estrogen Receptor Antagonist

FDA label (Established Pharmacologic Class)

Who reports

32,837 reports · 81% serious · 4,960 with death outcome · 99% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Fulvestrant Injection is an estrogen receptor antagonist indicated for the treatment of: Hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer in postmenopausal women not previously treated with endocrine therapy. ( 1 ) HR-positive advanced breast cancer in postmenopausal women with disease progression following endocrine therapy.

FDA label, Indications and Usage

What it is

Fulvestrant Injection for intramuscular administration is an estrogen receptor antagonist.

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 3Lab value / disease marker 7Not in label — unassessed 29

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). 1,154 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Pik3ca-activated mutation	167	677.8 544.8–843.2ROR 681.2 · calibrated p 4e-15 ✓	315.0 EB05 276.9 · IC025 +7.1 3/3 methods agree	Not in label — unassessed	serious n=166	not reported in cached trials
Hormone receptor positive her2 negative breast cancer	126	430.8 343.5–540.2ROR 432.4 · calibrated p 5e-13 ✓	246.5 EB05 212.5 · IC025 +6.7 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious n=126 · 92% clinician	not reported in cached trials
Carbohydrate antigen 15-3 increased	251	315.2 271.0–366.6ROR 317.6 · calibrated p 7e-12 ✓	207.0 EB05 186.4 · IC025 +7.0 3/3 methods agree	Lab value / disease marker	serious n=248	not reported in cached trials
Elliptocytosis	26	259.6 164.4–409.9ROR 259.8 · calibrated p 3e-10 ✓	162.3 EB05 116.4 · IC025 +4.7 3/3 methods agree	Not in label — unassessed	serious n=25	not reported in cached trials
Carbohydrate antigen 27.29 increased	38	215.4 149.0–311.2ROR 215.6 · calibrated p 7e-10 ✓	148.8 EB05 113.2 · IC025 +5.2 3/3 methods agree	Lab value / disease marker	serious n=28	not reported in cached trials
Pseudocirrhosis	79	202.8 157.4–261.3ROR 203.3 · calibrated p 6e-10 ✓	148.2 EB05 122.7 · IC025 +5.9 3/3 methods agree	Not in label — unassessed	serious n=79 · 100% clinician	not reported in cached trials
Infusion site coldness	24	201.3 127.1–318.7ROR 201.5 · calibrated p 2e-9 ✓	136.4 EB05 96.5 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=24 · 100% clinician	not reported in cached trials
Metastases to thorax	47	144.9 105.6–199.0ROR 145.1 · calibrated p 1e-8 ✓	112.7 EB05 88.2 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious n=47	not reported in cached trials
Metastases to eye	39	137.1 97.0–193.8ROR 137.2 · calibrated p 2e-8 ✓	106.9 EB05 81.6 · IC025 +5.0 3/3 methods agree	Not in label — unassessed	serious n=39	NCT01610284: 1/570 (0.2%) control (serious AE)
Pleural neoplasm	29	136.1 91.1–203.4ROR 136.3 · calibrated p 3e-8 ✓	104.6 EB05 76.4 · IC025 +4.7 3/3 methods agree	Not in label — unassessed	serious n=29 · 100% clinician	not reported in cached trials
Metastases to spinal cord	33	130.6 89.8–189.9ROR 130.7 · calibrated p 4e-8 ✓	102.0 EB05 76.0 · IC025 +4.8 3/3 methods agree	Not in label — unassessed	serious n=33 · 100% clinician	not reported in cached trials
Metastases to pleura	166	121.1 102.6–143.0ROR 121.8 · calibrated p 3e-8 ✓	100.6 EB05 88.4 · IC025 +6.0 3/3 methods agree	Not in label — unassessed	serious n=166	not reported in cached trials
Tumour marker abnormal	53	119.9 89.4–160.9ROR 120.1 · calibrated p 5e-8 ✓	97.4 EB05 77.3 · IC025 +5.2 3/3 methods agree	Lab value / disease marker	serious n=42	not reported in cached trials
Metastases to skin	160	118.3 99.9–140.0ROR 118.9 · calibrated p 4e-8 ✓	98.6 EB05 86.4 · IC025 +6.0 3/3 methods agree	Not in label — unassessed	serious n=159	not reported in cached trials
Breast cancer metastatic	1,645	115.7 109.9–121.8ROR 121.8 · calibrated p 2e-8 ✓	97.8 EB05 93.9 · IC025 +6.5 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 69.6	not reported in cached trials
Tumour marker increased	666	102.6 94.6–111.3ROR 104.7 · calibrated p 8e-8 ✓	88.2 EB05 82.7 · IC025 +6.2 3/3 methods agree	Lab value / disease marker	serious n=566	not reported in cached trials
Metastases to breast	43	96.6 70.1–133.2ROR 96.7 · calibrated p 3e-7 ✓	81.0 EB05 62.6 · IC025 +4.9 3/3 methods agree	Not in label — unassessed	serious n=43	not reported in cached trials
Metastases to bone	2,131	95.7 91.5–100.0ROR 102.2 · calibrated p 1e-7 ✓	83.1 EB05 80.2 · IC025 +6.3 3/3 methods agree	Not in label — unassessed	serious PRR 59.9	NCT01610284: 1/570 (0.2%) control (serious AE)
Metastases to chest wall	45	95.3 69.7–130.4ROR 95.4 · calibrated p 3e-7 ✓	80.2 EB05 62.4 · IC025 +5.0 3/3 methods agree	Not in label — unassessed	serious n=45	not reported in cached trials
Gamma-glutamyltransferase decreased	24	90.4 58.9–138.7ROR 90.5 · calibrated p 7e-7 ✓	74.6 EB05 52.8 · IC025 +4.2 3/3 methods agree	Lab value / disease marker	serious n=24 · 100% clinician	NCT01610284: 1/570 (0.2%) control (serious AE)
Nail bed inflammation	39	89.2 63.8–124.7ROR 89.3 · calibrated p 5e-7 ✓	75.5 EB05 57.6 · IC025 +4.8 3/3 methods agree	Not in label — unassessed	serious n=37 · 100% clinician	not reported in cached trials
Tumour marker decreased	22	88.2 56.4–137.7ROR 88.2 · calibrated p 1e-6 ✓	72.7 EB05 50.6 · IC025 +4.1 3/3 methods agree	Lab value / disease marker	serious n=20	not reported in cached trials
Musculoskeletal toxicity	21	82.1 52.1–129.3ROR 82.1 · calibrated p 2e-6 ✓	68.4 EB05 47.2 · IC025 +4.0 3/3 methods agree	Labeled (related wording) related wording	serious n=20 · 100% clinician	not reported in cached trials
Hormone receptor positive breast cancer	27	72.9 48.9–108.6ROR 73.0 · calibrated p 3e-6 ✓	62.7 EB05 45.2 · IC025 +4.3 3/3 methods agree	Likely indication confounding term in indications	serious n=27 · 100% clinician	not reported in cached trials
Chest wall mass	26	71.1 47.4–106.7ROR 71.2 · calibrated p 3e-6 ✓	61.3 EB05 43.9 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=26 · 100% clinician	not reported in cached trials
Adnexa uteri mass	28	71.0 48.1–105.0ROR 71.1 · calibrated p 3e-6 ✓	61.4 EB05 44.6 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious n=28 · 100% clinician	not reported in cached trials
Metastases to liver	1,737	70.2 66.9–73.7ROR 74.1 · calibrated p 1e-6 ✓	63.2 EB05 60.7 · IC025 +5.9 3/3 methods agree	Not in label — unassessed	serious PRR 45.3	not reported in cached trials
Breast cancer recurrent	305	68.4 60.8–76.9ROR 69.0 · calibrated p 2e-6 ✓	61.5 EB05 56.0 · IC025 +5.6 3/3 methods agree	Not in label — unassessed	serious n=301	not reported in cached trials
Intestinal metastasis	34	68.3 48.0–97.3ROR 68.4 · calibrated p 3e-6 ✓	59.8 EB05 44.7 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=34	not reported in cached trials
Metastases to the mediastinum	39	66.1 47.6–92.0ROR 66.2 · calibrated p 4e-6 ✓	58.3 EB05 44.5 · IC025 +4.6 3/3 methods agree	Not in label — unassessed	serious n=39 · 100% clinician	not reported in cached trials
Metastases to pelvis	59	65.8 50.3–86.0ROR 65.9 · calibrated p 3e-6 ✓	58.6 EB05 47.1 · IC025 +4.9 3/3 methods agree	Not in label — unassessed	serious n=59	not reported in cached trials
Metastases to spine	310	65.0 57.9–73.1ROR 65.7 · calibrated p 2e-6 ✓	58.8 EB05 53.5 · IC025 +5.6 3/3 methods agree	Not in label — unassessed	serious n=309	not reported in cached trials
Metastases to ovary	28	61.8 41.9–91.1ROR 61.9 · calibrated p 7e-6 ✓	54.4 EB05 39.5 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=28	not reported in cached trials
Oestradiol increased	25	58.2 38.7–87.7ROR 58.3 · calibrated p 1e-5 ✓	51.4 EB05 36.6 · IC025 +4.1 3/3 methods agree	Lab value / disease marker	–	not reported in cached trials
Bone marrow infiltration	32	57.7 40.2–82.8ROR 57.7 · calibrated p 1e-5 ✓	51.4 EB05 38.1 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious n=32 · 100% clinician	not reported in cached trials
Nasal mucosal disorder	47	55.8 41.4–75.2ROR 55.9 · calibrated p 1e-5 ✓	50.3 EB05 39.4 · IC025 +4.6 3/3 methods agree	Not in label — unassessed	serious n=47	not reported in cached trials
Invasive lobular breast carcinoma	41	55.5 40.3–76.3ROR 55.5 · calibrated p 1e-5 ✓	49.9 EB05 38.4 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=39 · 100% clinician	not reported in cached trials
Poikilocytosis	21	52.4 33.6–81.8ROR 52.5 · calibrated p 2e-5 ✓	46.6 EB05 32.1 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious n=20	not reported in cached trials
Invasive breast carcinoma	30	49.9 34.4–72.4ROR 50.0 · calibrated p 3e-5 ✓	45.1 EB05 33.1 · IC025 +4.1 3/3 methods agree	Not in label — unassessed	serious n=30 · 100% clinician	not reported in cached trials
Bone lesion	254	48.3 42.5–54.9ROR 48.7 · calibrated p 2e-5 ✓	44.8 EB05 40.4 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious n=249	not reported in cached trials

Trial evidence (ClinicalTrials.gov)

✓ Trial adverse-event data found on ClinicalTrials.gov

Largest completed trials with posted results that list Fulvestrant 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 (3 of 40 signal terms matched).

NCT01610284 — Phase III Study of BKM120/Placebo With Fulvestrant in Postmenopausal Patients With Hormone Receptor Positive H (N=1147, PHASE3; 255 AE terms posted; arms: BKM120 100 mg + Fulvestrant; Placebo + Fulvestrant)
NCT04975308 — A Study of Imlunestrant, Investigator's Choice of Endocrine Therapy, and Imlunestrant Plus Abemaciclib in Part (N=874, PHASE3; 178 AE terms posted; arms: Arm A: Imlunestrant; Arm B: Investigator's Choice of Endocrin; Arm B: Investigator's Choice of Endocrin; Arm C: Imlunestrant + Abemaciclib)

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
Malignant neoplasm progression	4,229	27.6 26.8–28.4ROR 31.6 · calibrated p 2e-4 ✓	26.5 EB05 25.8 · IC025 +4.7 3/3 methods agree	Reporting / coding artifact	serious PRR 19.2	not reported in cached trials
Fatigue (tiredness)	4,182	3.5 3.4–3.6ROR 3.8 · calibrated p 0.415	3.4 EB05 3.3 · IC025 +1.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.3	NCT01610284: 7/573 (1.2%) on Fulvestrant (serious AE)
Nausea	3,029	2.5 2.4–2.5ROR 2.6 · calibrated p 0.769	2.5 EB05 2.4 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.6	NCT01610284: 4/573 (0.7%) on Fulvestrant; 2/570 (0.4%) control (serious AE)
Death	2,742	2.0 2.0–2.1ROR 2.1 · calibrated p 0.987	2.0 EB05 2.0 · IC025 +1.0	Outcome field, not a reaction	serious PRR 1.5	NCT01610284: 1/573 (0.2%) on Fulvestrant (serious AE)
Diarrhoea (diarrhea)	2,623	2.6 2.5–2.7ROR 2.8 · calibrated p 0.713	2.6 EB05 2.5 · IC025 +1.3 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.5	NCT01610284: 7/573 (1.2%) on Fulvestrant; 2/570 (0.4%) control (serious AE)
Neutropenia (low neutrophils (infection-fighting cells))	2,485	11.9 11.5–12.4ROR 12.8 · calibrated p 0.013 ✓	11.7 EB05 11.3 · IC025 +3.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.5	NCT01610284: 1/573 (0.2%) on Fulvestrant; 1/570 (0.2%) control (serious AE)
White blood cell count decreased	2,199	13.2 12.7–13.7ROR 14.1 · calibrated p 0.009 ✓	12.9 EB05 12.5 · IC025 +3.6 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 8.5	NCT04975308: 17/292 (5.8%) on Fulvestrant
Metastases to bone	2,131	95.7 91.5–100.0ROR 102.2 · calibrated p 1e-7 ✓	83.1 EB05 80.2 · IC025 +6.3 3/3 methods agree	Not in label — unassessed	serious PRR 59.9	NCT01610284: 1/570 (0.2%) control (serious AE)
Neoplasm progression	2,129	41.2 39.5–43.0ROR 44.0 · calibrated p 3e-5 ✓	38.7 EB05 37.3 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious PRR 28.0	not reported in cached trials
Asthenia (weakness)	1,771	3.0 2.9–3.2ROR 3.1 · calibrated p 0.585	3.0 EB05 2.9 · IC025 +1.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.6	NCT01610284: 7/573 (1.2%) on Fulvestrant; 2/570 (0.4%) control (serious AE)
Pain	1,758	1.8 1.7–1.9ROR 1.9 · calibrated p 0.873	1.8 EB05 1.8 · IC025 +0.8	Labeled adverse reaction exact term	serious PRR 1.7	NCT01610284: 2/573 (0.3%) on Fulvestrant; 3/570 (0.5%) control (serious AE)
Metastases to liver	1,737	70.2 66.9–73.7ROR 74.1 · calibrated p 1e-6 ✓	63.2 EB05 60.7 · IC025 +5.9 3/3 methods agree	Not in label — unassessed	serious PRR 45.3	not reported in cached trials
Breast cancer metastatic	1,645	115.7 109.9–121.8ROR 121.8 · calibrated p 2e-8 ✓	97.8 EB05 93.9 · IC025 +6.5 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 69.6	not reported in cached trials
Dyspnoea (shortness of breath)	1,633	1.8 1.8–1.9ROR 1.9 · calibrated p 0.883	1.8 EB05 1.8 · IC025 +0.8	Labeled adverse reaction exact term	serious PRR 1.6	NCT01610284: 4/573 (0.7%) on Fulvestrant; 3/570 (0.5%) control (serious AE)
Vomiting	1,577	2.2 2.1–2.3ROR 2.2 · calibrated p 0.947	2.1 EB05 2.1 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.0	NCT01610284: 7/573 (1.2%) on Fulvestrant; 5/570 (0.9%) control (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=167, PRR 677.8
Elliptocytosis — n=26, PRR 259.6
Pseudocirrhosis — n=79, PRR 202.8
Infusion site coldness — n=24, PRR 201.3
Metastases to thorax — n=47, PRR 144.9
Metastases to eye — n=39, PRR 137.1 (also seen in trial arm)
Pleural neoplasm — n=29, PRR 136.1
Metastases to spinal cord — n=33, PRR 130.6
Metastases to pleura — n=166, PRR 121.1
Metastases to skin — n=160, PRR 118.3

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 Fulvestrant?

In FDA FAERS, the most frequently co-reported reaction terms for Fulvestrant are fatigue, nausea, diarrhoea, neutropenia, white blood cell count decreased, metastases to bone. 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 Fulvestrant have an FDA boxed warning?

No. The FDA label retrieved for Fulvestrant has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Fulvestrant 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 015fafb6-23f7-4566-9c23-386eee7b035d, effective 20240617; matched on openfda.generic_name.exact:"FULVESTRANT")
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, field patient.drug.openfda.generic_name.exact, 1,194 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 FULVESTRANT, 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.