Fentanyl Citrate side effects: what 17,767 FDA adverse event reports show

Fentanyl Citrate · Fentanyl System · 1,065 reaction terms · 56,202 drug–reaction co-reports · data 2026-09-14

Drug class

Opioid Agonist

FDA label (Established Pharmacologic Class) · compare the class

Brand names

Fentanyl System

openFDA label

Who reports

17,767 reports · 88% serious · 6,170 with death outcome · 48% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Fentanyl transdermal system is indicated for the management of severe and persistent pain in opioid-tolerant patients, that requires an opioid analgesic and that cannot be adequately treated with alternative options, including immediate-release opioids.

FDA label, Indications and Usage

What it is

The system contains fentanyl, an opioid agonist, for transdermal administration. The amount of fentanyl released from each system per hour is proportional to the surface area (25 mcg/hour per 9.44 cm 2 ). The composition per unit area of all transdermal system sizes is identical.

FDA label, Description section

Boxed warning

SERIOUS AND LIFE-THREATENING RISKS FROM USE OF FENTANYL TRANSDERMAL SYSTEM . WARNING: SERIOUS AND LIFE-THREATENING RISKS FROM USE OF FENTANYL TRANSDERMAL SYSTEM See full prescribing information for complete boxed warning. Fentanyl transdermal system exposes users to risks of addiction, abuse, and misuse, which can lead to overdose and death.

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 adverse reaction 3Labeled (related wording) 3Reporting / coding artifact 7Lab value / disease marker 4Not in label — unassessed 22

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 adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
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 flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 1,025 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
Vaginal flatulence	72	364.3 279.7–474.5ROR 365.8 · χ² 19,593 / p <1e-300	258.7 EB05 212.3 · IC025 +6.2 3/3 methods agree	Not in label — unassessed	serious n=72 · ♀ 100% (drug 48%)	no trial arm names this drug
Chanter syndrome	11	158.1 84.2–296.7ROR 158.2 · χ² 1,376 / p <1e-300	112.6 EB05 67.1 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious n=11	no trial arm names this drug
Anterior spinal artery syndrome	10	157.3 81.3–304.4ROR 157.4 · χ² 1,234 / p 1e-270	110.1 EB05 63.9 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious n=10	no trial arm names this drug
Burkholderia test positive	13	137.5 77.4–244.4ROR 137.6 · χ² 1,456 / p <1e-300	104.6 EB05 65.1 · IC025 +3.5 3/3 methods agree	Lab value / disease marker	serious n=13	no trial arm names this drug
Dependence	3,935	90.0 87.4–92.6ROR 115.3 · χ² 322,217 / p <1e-300	83.6 EB05 81.4 · IC025 +6.3 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 54.8 · 100% consumer	no trial arm names this drug
Substance dependence	47	89.1 66.2–119.8ROR 89.3 · χ² 3,721 / p <1e-300	80.2 EB05 62.8 · IC025 +5.0 3/3 methods agree	Labeled (related wording) related wording	serious n=47 · 83% consumer	no trial arm names this drug
Narcotic intoxication	17	82.1 50.2–134.2ROR 82.2 · χ² 1,197 / p 1e-262	70.9 EB05 46.9 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious n=17	no trial arm names this drug
Learning disorder	139	71.3 60.1–84.6ROR 71.9 · χ² 9,017 / p <1e-300	66.7 EB05 57.9 · IC025 +5.5 3/3 methods agree	Not in label — unassessed	serious n=139 · 100% consumer	no trial arm names this drug
Neuromuscular block prolonged	19	63.5 40.1–100.8ROR 63.6 · χ² 1,051 / p 9e-231	57.0 EB05 38.6 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious n=18	no trial arm names this drug
Speech disorder developmental	138	59.3 50.0–70.3ROR 59.7 · χ² 7,470 / p <1e-300	56.0 EB05 48.6 · IC025 +5.3 3/3 methods agree	Not in label — unassessed	serious n=138 · 100% consumer	no trial arm names this drug
Female genital tract fistula	77	55.3 44.0–69.4ROR 55.5 · χ² 3,865 / p <1e-300	52.2 EB05 43.1 · IC025 +4.9 3/3 methods agree	Not in label — unassessed	serious n=77 · ♀ 100% (drug 48%)	no trial arm names this drug
Amnestic disorder	19	48.7 30.8–77.1ROR 48.8 · χ² 807 / p 8e-178	44.8 EB05 30.3 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious n=17	no trial arm names this drug
Delayed recovery from anaesthesia	31	39.9 27.9–57.0ROR 39.9 · χ² 1,099 / p 3e-241	37.8 EB05 27.9 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious n=29 · 100% clinician	no trial arm names this drug
Hepatic ischaemia	10	39.1 20.8–73.3ROR 39.1 · χ² 323 / p 2e-72	35.5 EB05 20.5 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious n=10	no trial arm names this drug
Procedural hypotension	27	38.4 26.2–56.3ROR 38.4 · χ² 915 / p 2e-201	36.3 EB05 26.2 · IC025 +3.8 3/3 methods agree	Not in label — unassessed	serious n=17 · ♀ 25% (drug 48%) · 100% clinician	no trial arm names this drug
Anion gap	20	38.0 24.4–59.4ROR 38.1 · χ² 663 / p 2e-146	35.7 EB05 24.4 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=20 · 100% clinician	no trial arm names this drug
Radiculopathy	78	36.0 28.7–45.0ROR 36.1 · χ² 2,538 / p <1e-300	34.6 EB05 28.7 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=78 · ♀ 100% (drug 48%)	no trial arm names this drug
Postmortem blood drug level increased	10	33.4 17.8–62.7ROR 33.5 · χ² 275 / p 4e-62	30.8 EB05 17.8 · IC025 +2.6 3/3 methods agree	Lab value / disease marker	serious n=10	no trial arm names this drug
Opiates positive	13	32.5 18.8–56.5ROR 32.6 · χ² 356 / p 8e-80	30.4 EB05 18.9 · IC025 +3.0 3/3 methods agree	Lab value / disease marker	serious n=13	no trial arm names this drug
Respiratory arrest	737	32.1 29.9–34.5ROR 33.5 · χ² 21,619 / p <1e-300	31.3 EB05 29.4 · IC025 +4.8 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 20.4 · 98% clinician	no trial arm names this drug
Hyperthermia malignant	39	32.0 23.3–44.0ROR 32.1 · χ² 1,110 / p 1e-243	30.7 EB05 23.5 · IC025 +4.0 3/3 methods agree	Labeled (related wording) related wording	serious n=39 · ♀ 24% (drug 48%) · 100% clinician	no trial arm names this drug
Proctitis	74	32.0 25.4–40.3ROR 32.1 · χ² 2,131 / p <1e-300	30.9 EB05 25.4 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious n=74 · ♀ 100% (drug 48%)	no trial arm names this drug
Substance use	39	30.6 22.3–42.1ROR 30.7 · χ² 1,060 / p 6e-233	29.5 EB05 22.5 · IC025 +3.9 3/3 methods agree	Reporting / coding artifact	serious n=39 · 100% clinician	no trial arm names this drug
Attention deficit hyperactivity disorder	92	26.7 –ROR 26.9 · χ² –	–	Not in label — unassessed	serious n=92 · 96% consumer	no trial arm names this drug
Drug withdrawal syndrome neonatal	320	25.8 23.1–28.8ROR 26.2 · χ² 7,440 / p <1e-300	25.2 EB05 23.0 · IC025 +4.4 3/3 methods agree	Labeled (related wording) related wording	serious PRR 16.5 · 97% consumer	no trial arm names this drug
Toxicologic test abnormal	13	25.6 14.8–44.3ROR 25.6 · χ² 277 / p 2e-62	24.2 EB05 14.9 · IC025 +2.8 3/3 methods agree	Reporting / coding artifact	serious n=13	no trial arm names this drug
Ill-defined disorder	1,288	25.5 24.2–26.9ROR 27.5 · χ² 29,773 / p <1e-300	25.0 EB05 23.9 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious PRR 24.5 · 99% consumer	no trial arm names this drug
Drug abuse	1,734	25.0 23.9–26.1ROR 27.6 · χ² 39,197 / p <1e-300	24.5 EB05 23.5 · IC025 +4.5 3/3 methods agree	Reporting / coding artifact	serious PRR 16.1 · 93% clinician	no trial arm names this drug
Toxic leukoencephalopathy	15	24.9 14.9–41.5ROR 24.9 · χ² 314 / p 2e-70	23.7 EB05 15.1 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious n=15	no trial arm names this drug
Blood pressure measurement	13	24.4 14.1–42.3ROR 24.5 · χ² 264 / p 1e-59	23.1 EB05 14.2 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious n=13	no trial arm names this drug
Hypermobility syndrome	10	24.3 13.0–45.4ROR 24.3 · χ² 197 / p 6e-45	22.6 EB05 12.7 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious n=10	no trial arm names this drug
Chronic sinusitis	74	23.8 18.9–29.9ROR 23.9 · χ² 1,559 / p <1e-300	23.2 EB05 19.1 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious n=74 · ♀ 100% (drug 48%)	no trial arm names this drug
Respiratory depression	231	22.6 19.9–25.8ROR 22.9 · χ² 4,670 / p <1e-300	22.2 EB05 19.9 · IC025 +4.2 3/3 methods agree	Labeled — boxed warning exact term	serious PRR 14.5	no trial arm names this drug
Product counterfeit	31	22.2 15.5–31.6ROR 22.2 · χ² 595 / p 1e-131	21.5 EB05 15.9 · IC025 +3.4 3/3 methods agree	Reporting / coding artifact	serious n=31 · 100% clinician	no trial arm names this drug
Sedation complication	46	22.1 16.5–29.6ROR 22.2 · χ² 889 / p 1e-195	21.5 EB05 16.8 · IC025 +3.7 3/3 methods agree	Reporting / coding artifact	serious n=19 · 96% clinician	no trial arm names this drug
Anaesthetic complication	47	21.1 15.8–28.2ROR 21.2 · χ² 865 / p 2e-190	20.6 EB05 16.1 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	serious n=33 · ♀ 74% (drug 48%) · 94% clinician	no trial arm names this drug
Analgesic drug level increased	27	20.0 13.7–29.3ROR 20.1 · χ² 461 / p 1e-102	19.4 EB05 13.9 · IC025 +3.2 3/3 methods agree	Lab value / disease marker	serious n=27 · 100% clinician	no trial arm names this drug
Developmental delay	146	19.2 16.3–22.6ROR 19.4 · χ² 2,466 / p <1e-300	18.9 EB05 16.5 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious PRR 12.5 · 100% consumer	no trial arm names this drug
Incorrect route of product administration	261	18.6 16.5–21.0ROR 18.9 · χ² 4,267 / p <1e-300	18.3 EB05 16.5 · IC025 +3.9 3/3 methods agree	Reporting / coding artifact	serious PRR 23.8 · 97% clinician	no trial arm names this drug
Labile blood pressure	18	18.1 11.4–28.9ROR 18.2 · χ² 270 / p 5e-61	17.4 EB05 11.3 · IC025 +2.8 3/3 methods agree	Labeled adverse reaction exact term	serious n=18	no trial arm names this drug

Trial evidence (ClinicalTrials.gov)

ClinicalTrials.gov returned results-bearing trials mentioning Fentanyl only as a background or rescue medication (NCT02625181, NCT00699335); 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
Dependence	3,935	90.0 87.4–92.6ROR 115.3 · χ² 322,217 / p <1e-300	83.6 EB05 81.4 · IC025 +6.3 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 54.8 · 100% consumer	no trial arm names this drug
Overdose	2,452	13.5 13.0–14.0ROR 15.5 · χ² 28,346 / p <1e-300	13.4 EB05 12.9 · IC025 +3.7 3/3 methods agree	Reporting / coding artifact	serious PRR 10.9 · 73% consumer	no trial arm names this drug
Death	2,062	2.8 2.7–2.9ROR 3.1 · χ² 2,538 / p <1e-300	2.8 EB05 2.7 · IC025 +1.4 3/3 methods agree	Outcome field, not a reaction boxed warning mentions mortality	serious PRR 1.8	no trial arm names this drug
Drug abuse	1,734	25.0 23.9–26.1ROR 27.6 · χ² 39,197 / p <1e-300	24.5 EB05 23.5 · IC025 +4.5 3/3 methods agree	Reporting / coding artifact	serious PRR 16.1 · 93% clinician	no trial arm names this drug
Toxicity to various agents	1,383	9.8 9.3–10.3ROR 10.5 · χ² 10,917 / p <1e-300	9.7 EB05 9.3 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious PRR 6.5 · 93% clinician	no trial arm names this drug
Ill-defined disorder	1,288	25.5 24.2–26.9ROR 27.5 · χ² 29,773 / p <1e-300	25.0 EB05 23.9 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious PRR 24.5 · 99% consumer	no trial arm names this drug
Cardiac arrest (heart stopping)	915	13.2 12.4–14.0ROR 13.8 · χ² 10,204 / p <1e-300	13.0 EB05 12.3 · IC025 +3.6 3/3 methods agree	Labeled (related wording) related wording	serious PRR 8.5 · 96% clinician	no trial arm names this drug
Respiratory arrest	737	32.1 29.9–34.5ROR 33.5 · χ² 21,619 / p <1e-300	31.3 EB05 29.4 · IC025 +4.8 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 20.4 · 98% clinician	no trial arm names this drug
Drug ineffective (drug did not work)	712	0.6 0.6–0.7ROR 0.6 · χ² 155 / p 6e-36	0.6 EB05 0.6 · IC025 -0.8 PRR-only: not supported by EBGM or IC	Reporting / coding artifact	serious PRR 0.8	no trial arm names this drug
Drug hypersensitivity	628	3.8 3.5–4.1ROR 3.9 · χ² 1,316 / p 2e-288	3.8 EB05 3.6 · IC025 +1.8 3/3 methods agree	Labeled (related wording) related wording	serious PRR 0.8 · ♀ 74% (drug 48%)	no trial arm names this drug
Nausea	603	0.9 0.8–1.0ROR 0.9 · χ² 7 / p 0.005	0.9 EB05 0.8 · IC025 -0.3 PRR-only: not supported by EBGM or IC	Labeled adverse reaction exact term	serious PRR 0.9 · ♀ 68% (drug 48%)	no trial arm names this drug
Pain	572	1.1 1.0–1.2ROR 1.1 · χ² 5 / p 0.013	1.1 EB05 1.0 · IC025 -0.0 PRR-only: not supported by EBGM or IC	Likely indication confounding term in indications; also in warnings	serious PRR 0.9	no trial arm names this drug
Wrong technique in drug usage process	487	15.8 14.5–17.3ROR 16.2 · χ² 6,657 / p <1e-300	15.6 EB05 14.5 · IC025 +3.8 3/3 methods agree	Reporting / coding artifact	serious PRR 9.8 · 75% consumer	no trial arm names this drug
Accidental overdose	457	14.9 13.6–16.4ROR 15.3 · χ² 5,863 / p <1e-300	14.7 EB05 13.6 · IC025 +3.7 3/3 methods agree	Reporting / coding artifact	serious PRR 15.8 · ♀ 28% (drug 48%) · 91% clinician	no trial arm names this drug
Off label use (used outside approved label)	453	0.6 0.6–0.7ROR 0.6 · χ² 113 / p 1e-26	0.6 EB05 0.6 · IC025 -0.9 PRR-only: not supported by EBGM or IC	Reporting / coding artifact	serious PRR 0.6 · ♀ 69% (drug 48%)	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.

Vaginal flatulence — n=72, PRR 364.3
Learning disorder — n=139, PRR 71.3
Speech disorder developmental — n=138, PRR 59.3
Female genital tract fistula — n=77, PRR 55.3
Delayed recovery from anaesthesia — n=31, PRR 39.9
Procedural hypotension — n=27, PRR 38.4
Anion gap — n=20, PRR 38.0
Radiculopathy — n=78, PRR 36.0
Proctitis — n=74, PRR 32.0
Attention deficit hyperactivity disorder — n=92, PRR 26.7

✓ A hand-written Bradford Hill causality assessment exists for this drug: Fentanyl (opioids) ↔ Respiratory depression.

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 Fentanyl?

In FDA FAERS, the most frequently co-reported reaction terms for Fentanyl are dependence, toxicity to various agents, ill-defined disorder, cardiac arrest, respiratory arrest, drug hypersensitivity. 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 Fentanyl have an FDA boxed warning?

Yes. The current FDA label carries a boxed warning: SERIOUS AND LIFE-THREATENING RISKS FROM USE OF FENTANYL TRANSDERMAL SYSTEM . WARNING: SERIOUS AND LIFE-THREATENING RISKS FROM USE OF FENTANYL TRANSDERMAL SYSTEM See full prescribing information for complete boxed warning. Fentanyl transdermal system exposes users to risks of addiction, abuse, and misuse, which can lead to overdose and death.

Do FAERS signals prove that Fentanyl 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 242759ef-cb6d-4e3e-9f8d-5e31efa1f289, effective 20260302; matched on openfda.generic_name.exact:"FENTANYL")
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, 1,065 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 FENTANYL, results-bearing studies sorted by enrollment)

Page generated 2026-10-08. 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.