Fluorouracil side effects: what 76,905 FDA adverse event reports show

Fluorouracil · 1,293 reaction terms · 231,797 drug–reaction co-reports · data 2026-09-14

Drug class

Nucleoside Metabolic Inhibitor

FDA label (Established Pharmacologic Class) · compare the class

Who reports

76,905 reports · 95% serious · 10,861 with death outcome · 45% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Fluorouracil is indicated for the treatment of patients with: Fluorouracil is a nucleoside metabolic inhibitor indicated for the treatment of patients with • Adenocarcinoma of the Colon and Rectum ( 1.1 ) • Adenocarcinoma of the Breast ( 1.2 ) • Gastri.

FDA label, Indications and Usage

What it is

Fluorouracil injection, USP, a nucleoside metabolic inhibitor, is a colorless to yellow aqueous, sterile, nonpyrogenic injectable solution available in a pharmacy bulk package, a sterile preparation that contains doses for multiple patients for intravenous administration.

FDA label, Description section

Boxed warning

SERIOUS ADVERSE REACTIONS OR DEATH IN PATIENTS WITH COMPLETE DPD DEFICIENCY Increased Risk of Serious Adverse Reactions or Death in Patients with Complete DPD Deficiency Test patients for genetic variants of DPYD prior to initiating fluorouracil unless immediate treatment is necessary.

FDA 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 — boxed warning 1Labeled (related wording) 4Likely indication confounding 3Reporting / coding artifact 2Lab value / disease marker 2Not in label — unassessed 28

What the badges mean

Labeled — boxed warning The term (or its clinical synonym) appears in the FDA boxed warning: causality is regulator-recognised and considered serious.
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.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
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). 1,253 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
Ductal adenocarcinoma of pancreas	108	176.5 138.5–225.0ROR 176.8 · calibrated p 2e-9 ✓	104.9 EB05 89.3 · IC025 +5.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Likely indication confounding shares a disease stem with the indications wording	serious n=108	no trial arm names this drug
Colorectal cancer metastatic	561	88.6 80.6–97.5ROR 89.3 · calibrated p 3e-7 ✓	66.7 EB05 62.2 · IC025 +5.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 21.0 (17.6–24.9)	Not in label — unassessed	serious n=557 · 94% clinician	no trial arm names this drug
Portal venous gas	81	81.3 63.4–104.3ROR 81.4 · calibrated p 7e-7 ✓	61.8 EB05 51.3 · IC025 +5.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=81 · ♀ 0% (drug 45%) · 100% clinician	no trial arm names this drug
Oesophageal fistula	70	76.9 59.0–100.3ROR 77.0 · calibrated p 1e-6 ✓	59.1 EB05 48.3 · IC025 +5.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=70 · 100% clinician	no trial arm names this drug
Non-cirrhotic portal hypertension	77	73.2 56.9–94.2ROR 73.3 · calibrated p 2e-6 ✓	56.9 EB05 47.0 · IC025 +5.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 9.0 (6.3–12.8)	Not in label — unassessed	serious n=77 · ♀ 76% (drug 45%) · 100% clinician	no trial arm names this drug
Mucosal toxicity	55	68.9 51.2–92.6ROR 68.9 · calibrated p 3e-6 ✓	54.0 EB05 43.1 · IC025 +4.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 8.6 (5.7–12.9)	Labeled (related wording) related wording	serious n=55 · 93% clinician	no trial arm names this drug
Dihydropyrimidine dehydrogenase deficiency	42	66.2 47.2–92.8ROR 66.3 · calibrated p 4e-6 ✓	52.1 EB05 40.2 · IC025 +4.5 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 1.7 (1.2–2.4)	Labeled (related wording) related wording	serious n=39 · ♀ 100% (drug 45%)	no trial arm names this drug
Tumour perforation	55	58.5 43.7–78.3ROR 58.5 · calibrated p 8e-6 ✓	47.5 EB05 37.8 · IC025 +4.6 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 4.4 (3.1–6.2)	Not in label — unassessed	serious n=55 · 91% clinician	no trial arm names this drug
Rectal cancer metastatic	50	45.9 34.0–62.0ROR 45.9 · calibrated p 3e-5 ✓	38.8 EB05 30.6 · IC025 +4.4 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=50 · ♀ 0% (drug 45%) · 100% clinician	no trial arm names this drug
Arteriospasm coronary	550	44.1 40.3–48.2ROR 44.4 · calibrated p 3e-5 ✓	37.9 EB05 35.4 · IC025 +5.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 5.7 (5.1–6.4)	Not in label — unassessed	serious n=549 · 100% clinician	no trial arm names this drug
Skin toxicity	777	44.0 40.8–47.5ROR 44.5 · calibrated p 3e-5 ✓	37.9 EB05 35.7 · IC025 +5.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 7.7 (6.9–8.5)	Labeled (related wording) related wording	serious n=766 · 93% clinician	no trial arm names this drug
Gastrointestinal anastomotic leak	52	41.5 31.0–55.6ROR 41.5 · calibrated p 6e-5 ✓	35.6 EB05 28.2 · IC025 +4.3 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 6.0 (4.1–8.8)	Not in label — unassessed	serious n=52 · ♀ 0% (drug 45%) · 100% clinician	no trial arm names this drug
Anastomotic complication	43	38.0 27.6–52.4ROR 38.1 · calibrated p 1e-4 ✓	33.0 EB05 25.5 · IC025 +4.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 4.4 (3.0–6.6)	Reporting / coding artifact	serious n=43 · ♀ 0% (drug 45%) · 100% clinician	no trial arm names this drug
Acute promyelocytic leukaemia	125	37.9 31.5–45.8ROR 38.0 · calibrated p 8e-5 ✓	33.2 EB05 28.6 · IC025 +4.6 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 5.1 (4.0–6.5)	Not in label — unassessed	serious n=108 · ♀ 83% (drug 45%)	no trial arm names this drug
Anastomotic leak	84	37.3 29.7–46.9ROR 37.4 · calibrated p 9e-5 ✓	32.7 EB05 27.2 · IC025 +4.4 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 3.8 (2.9–5.0)	Not in label — unassessed	serious n=81 · 100% clinician	no trial arm names this drug
Dermatitis acneiform	689	35.0 32.3–37.8ROR 35.3 · calibrated p 1e-4 ✓	31.0 EB05 29.1 · IC025 +4.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 23.4 (19.9–27.6)	Not in label — unassessed	serious n=653 · 93% clinician	no trial arm names this drug
Focal nodular hyperplasia	58	33.7 25.6–44.2ROR 33.7 · calibrated p 2e-4 ✓	29.7 EB05 23.9 · IC025 +4.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=58 · 100% clinician	no trial arm names this drug
Hepatectomy	33	33.0 23.0–47.4ROR 33.0 · calibrated p 2e-4 ✓	29.1 EB05 21.7 · IC025 +3.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=33	no trial arm names this drug
Bacterial translocation	34	32.7 22.9–46.6ROR 32.7 · calibrated p 3e-4 ✓	28.8 EB05 21.6 · IC025 +3.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=34 · 100% clinician	no trial arm names this drug
Nodular regenerative hyperplasia	75	32.1 25.2–40.7ROR 32.1 · calibrated p 2e-4 ✓	28.6 EB05 23.5 · IC025 +4.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 10.9 (7.5–15.9)	Not in label — unassessed	serious n=74 · 100% clinician	no trial arm names this drug
Rectal perforation	55	30.8 23.3–40.8ROR 30.9 · calibrated p 3e-4 ✓	27.5 EB05 21.9 · IC025 +4.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 7.4 (5.0–11.0)	Not in label — unassessed	serious n=54	no trial arm names this drug
Rectal adenocarcinoma	57	28.7 21.8–37.7ROR 28.7 · calibrated p 4e-4 ✓	25.8 EB05 20.6 · IC025 +4.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Likely indication confounding shares a disease stem with the indications wording	serious n=57 · 91% clinician	no trial arm names this drug
Hyperammonaemic encephalopathy	161	28.2 24.0–33.2ROR 28.3 · calibrated p 4e-4 ✓	25.5 EB05 22.4 · IC025 +4.3 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 14.4 (10.9–19.1)	Not in label — unassessed	serious n=161 · 100% clinician	no trial arm names this drug
Cholinergic syndrome	60	28.0 21.5–36.6ROR 28.0 · calibrated p 5e-4 ✓	25.3 EB05 20.4 · IC025 +4.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=60 · 93% clinician	no trial arm names this drug
Gastrointestinal toxicity	420	26.6 24.1–29.4ROR 26.8 · calibrated p 5e-4 ✓	24.3 EB05 22.4 · IC025 +4.4 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 3.4 (3.0–3.9)	Labeled (related wording) related wording	serious n=417 · 98% clinician	no trial arm names this drug
Device related thrombosis	86	26.1 20.9–32.6ROR 26.2 · calibrated p 6e-4 ✓	23.8 EB05 19.9 · IC025 +4.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 5.8 (4.3–7.7)	Reporting / coding artifact	serious n=85 · 95% clinician	no trial arm names this drug
Toxic leukoencephalopathy	60	24.5 18.8–31.9ROR 24.5 · calibrated p 9e-4 ✓	22.4 EB05 18.0 · IC025 +3.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 4.6 (3.3–6.4)	Not in label — unassessed	serious n=60 · 100% clinician	no trial arm names this drug
Adenocarcinoma of colon	155	24.5 20.8–28.9ROR 24.6 · calibrated p 8e-4 ✓	22.5 EB05 19.7 · IC025 +4.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 12.9 (9.8–17.1)	Likely indication confounding term in indications	serious n=155 · 97% clinician	no trial arm names this drug
Paronychia	357	24.4 21.9–27.2ROR 24.6 · calibrated p 8e-4 ✓	22.5 EB05 20.6 · IC025 +4.3 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 6.3 (5.5–7.3)	Not in label — unassessed	serious n=350 · 95% clinician	no trial arm names this drug
Carbohydrate antigen 19-9 increased	42	24.0 17.5–32.8ROR 24.0 · calibrated p 0.001 ✓	21.9 EB05 16.9 · IC025 +3.6 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Lab value / disease marker	serious n=39 · 90% clinician	no trial arm names this drug
Steatohepatitis	43	23.6 17.3–32.3ROR 23.6 · calibrated p 0.001 ✓	21.6 EB05 16.7 · IC025 +3.6 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=43 · ♀ 100% (drug 45%) · 100% clinician	no trial arm names this drug
Ileal perforation	53	23.5 17.8–31.1ROR 23.5 · calibrated p 0.001 ✓	21.6 EB05 17.1 · IC025 +3.7 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=53 · ♀ 0% (drug 45%)	no trial arm names this drug
Colon cancer metastatic	127	23.3 19.5–28.0ROR 23.4 · calibrated p 0.001 ✓	21.5 EB05 18.5 · IC025 +4.0 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 5.5 (4.3–7.0)	Not in label — unassessed	serious n=126	no trial arm names this drug
Neutropenic colitis	160	22.9 19.5–26.9ROR 22.9 · calibrated p 0.001 ✓	21.1 EB05 18.5 · IC025 +4.1 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 1.8 (1.5–2.1)	Not in label — unassessed	serious n=160 · 97% clinician	no trial arm names this drug
Radiation skin injury	87	22.0 17.7–27.4ROR 22.0 · calibrated p 0.001 ✓	20.3 EB05 17.0 · IC025 +3.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 4.7 (3.6–6.3)	Not in label — unassessed	serious n=78 · ♀ 66% (drug 45%)	no trial arm names this drug
Myocardial injury	73	21.6 17.0–27.4ROR 21.6 · calibrated p 0.002 ✓	19.9 EB05 16.4 · IC025 +3.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=73 · 100% clinician	no trial arm names this drug
Intravascular haemolysis	40	21.0 15.2–29.0ROR 21.0 · calibrated p 0.002 ✓	19.4 EB05 14.8 · IC025 +3.5 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Not in label — unassessed	serious n=40 · 100% clinician	no trial arm names this drug
Interleukin level increased	38	20.8 15.0–29.0ROR 20.8 · calibrated p 0.002 ✓	19.2 EB05 14.6 · IC025 +3.4 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: only this drug	Lab value / disease marker	serious n=37 · ♀ 0% (drug 45%)	no trial arm names this drug
Mucosal inflammation	1,806	20.2 19.3–21.2ROR 20.7 · calibrated p 0.002 ✓	18.9 EB05 18.2 · IC025 +4.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.6 (2.5–2.8)	Labeled — boxed warning synonym match	serious PRR 12.0 · 93% clinician	no trial arm names this drug
Metastases to peritoneum	172	20.0 17.2–23.4ROR 20.1 · calibrated p 0.002 ✓	18.7 EB05 16.5 · IC025 +3.9 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 4.2 (3.5–5.2)	Not in label — unassessed	serious n=171 · 94% clinician	no trial arm names this drug

Trial evidence (ClinicalTrials.gov)

ClinicalTrials.gov returned results-bearing trials mentioning Fluorouracil only as a background or rescue medication (NCT01358877, NCT02135419); no trial listing it as the tested intervention was cached, so no trial cross-check is shown.

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
Diarrhoea (diarrhea)	6,991	3.0 2.9–3.1ROR 3.2 · calibrated p 0.569	3.0 EB05 2.9 · IC025 +1.5 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.5 (2.5–2.6)	Labeled — boxed warning exact term	serious PRR 3.1 · 92% clinician	no trial arm names this drug
Neutropenia (low neutrophils (infection-fighting cells))	5,175	10.8 10.5–11.1ROR 11.5 · calibrated p 0.020 ✓	10.4 EB05 10.2 · IC025 +3.3 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 3.0 (2.9–3.1)	Labeled adverse reaction exact term	serious PRR 6.4 · 94% clinician	no trial arm names this drug
Nausea	5,001	1.7 1.7–1.8ROR 1.8 · calibrated p 0.820	1.7 EB05 1.7 · IC025 +0.7 vs other Nucleoside Metabolic Inhibitors: PRR 2.6 (2.5–2.7)	Labeled adverse reaction exact term	serious PRR 1.9 · 91% clinician	no trial arm names this drug
Vomiting	3,998	2.3 2.3–2.4ROR 2.4 · calibrated p 0.852	2.3 EB05 2.3 · IC025 +1.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.7 (2.6–2.8)	Labeled adverse reaction exact term	serious PRR 2.1 · 92% clinician	no trial arm names this drug
Off label use (used outside approved label)	3,606	1.1 1.1–1.2ROR 1.1 · calibrated p 0.399	1.1 EB05 1.1 · IC025 +0.1 vs other Nucleoside Metabolic Inhibitors: PRR 1.7 (1.6–1.8)	Reporting / coding artifact	serious PRR 1.2	no trial arm names this drug
Neuropathy peripheral (nerve damage in hands/feet)	3,378	10.1 9.7–10.4ROR 10.5 · calibrated p 0.027 ✓	9.7 EB05 9.5 · IC025 +3.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 5.3 (5.1–5.6)	Not in label — unassessed	serious PRR 6.8 · 91% clinician	no trial arm names this drug
Disease progression	3,255	7.7 7.5–8.0ROR 8.0 · calibrated p 0.066	7.5 EB05 7.3 · IC025 +2.9 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 1.9 (1.9–2.0)	Reporting / coding artifact	serious PRR 5.2 · 95% clinician	no trial arm names this drug
Fatigue (tiredness)	3,228	1.1 1.1–1.2ROR 1.1 · calibrated p 0.399	1.1 EB05 1.1 · IC025 +0.1 vs other Nucleoside Metabolic Inhibitors: PRR 2.4 (2.3–2.4)	Not in label — unassessed	serious PRR 1.2	no trial arm names this drug
Pyrexia (fever)	3,063	2.4 2.3–2.5ROR 2.5 · calibrated p 0.820	2.4 EB05 2.3 · IC025 +1.2 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 1.9 (1.9–2.0)	Not in label — unassessed	serious PRR 1.8 · 92% clinician	no trial arm names this drug
Thrombocytopenia (low platelets)	2,966	7.4 7.2–7.7ROR 7.7 · calibrated p 0.075	7.2 EB05 7.0 · IC025 +2.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.2 (2.1–2.2)	Labeled adverse reaction exact term	serious PRR 4.5 · 93% clinician	no trial arm names this drug
Febrile neutropenia	2,889	12.4 12.0–12.9ROR 12.8 · calibrated p 0.013 ✓	11.9 EB05 11.5 · IC025 +3.5 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 1.2 (1.2–1.2)	Labeled (related wording) related wording	serious PRR 7.2 · 95% clinician	no trial arm names this drug
Asthenia (weakness)	2,574	1.9 1.8–1.9ROR 1.9 · calibrated p 0.890	1.9 EB05 1.8 · IC025 +0.8 vs other Nucleoside Metabolic Inhibitors: PRR 3.0 (2.9–3.2)	Not in label — unassessed	serious PRR 1.6	no trial arm names this drug
Anaemia (low red blood cells)	2,548	3.7 3.5–3.8ROR 3.8 · calibrated p 0.424	3.6 EB05 3.5 · IC025 +1.8 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.4 (2.3–2.5)	Labeled adverse reaction exact term	serious PRR 2.4 · 93% clinician	no trial arm names this drug
Drug ineffective (drug did not work)	2,221	0.5 0.4–0.5ROR 0.4 · calibrated p 0.032 ✓	0.5 EB05 0.4 · IC025 -1.2 PRR-only: not supported by EBGM or IC vs other Nucleoside Metabolic Inhibitors: PRR 1.7 (1.6–1.8)	Reporting / coding artifact	serious PRR 0.7 · 92% clinician	no trial arm names this drug
Malignant neoplasm progression	2,172	5.9 5.7–6.2ROR 6.1 · calibrated p 0.146	5.8 EB05 5.6 · IC025 +2.5 3/3 methods agree vs other Nucleoside Metabolic Inhibitors: PRR 2.4 (2.3–2.5)	Reporting / coding artifact	serious PRR 3.6	no trial arm names this drug

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.

Colorectal cancer metastatic — n=561, PRR 88.6
Portal venous gas — n=81, PRR 81.3
Oesophageal fistula — n=70, PRR 76.9
Non-cirrhotic portal hypertension — n=77, PRR 73.2
Tumour perforation — n=55, PRR 58.5
Rectal cancer metastatic — n=50, PRR 45.9
Arteriospasm coronary — n=550, PRR 44.1
Gastrointestinal anastomotic leak — n=52, PRR 41.5
Acute promyelocytic leukaemia — n=125, PRR 37.9
Anastomotic leak — n=84, PRR 37.3

✓ A hand-written Bradford Hill causality assessment exists for this drug: Fluorouracil ↔ Neutropenia.

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 Fluorouracil?

In FDA FAERS, the most frequently co-reported reaction terms for Fluorouracil are diarrhoea, neutropenia, nausea, vomiting, neuropathy peripheral, fatigue. 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 Fluorouracil have an FDA boxed warning?

Yes. The current FDA label carries a boxed warning: SERIOUS ADVERSE REACTIONS OR DEATH IN PATIENTS WITH COMPLETE DPD DEFICIENCY Increased Risk of Serious Adverse Reactions or Death in Patients with Complete DPD Deficiency Test patients for genetic variants of DPYD prior to initiating fluorouracil unless immediate treatment is necessary.

Do FAERS signals prove that Fluorouracil 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 21af1777-87f7-4e40-9917-f1677e7ff1a5, effective 20260608; matched on openfda.generic_name.exact:"FLUOROURACIL")
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, 1,293 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 FLUOROURACIL, 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.