Drug · FAERS side-effect profile with label screen
Zanamivir side effects: what 2,524 FDA adverse event reports show
Drug class
Neuraminidase Inhibitor
FDA label (Established Pharmacologic Class)
Brand names
Relenza
openFDA label
Who reports
2,524 reports · 63% serious · 250 with death outcome · 52% female
openFDA FAERS counts, all years, deduplication not applied
Used for
RELENZA, an influenza virus neuraminidase inhibitor (NAI), is indicated for: Treatment of acute, uncomplicated influenza type A and B infections in patients aged 7 years and older who have been symptomatic for no more than 2 days. ( 1.1 ) Prophylaxis of influenza in patients aged 5 years and older.
FDA label, Indications and Usage
What it is
The active component of RELENZA is zanamivir.
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 adverse reaction 7Labeled (related wording) 4Likely indication confounding 1Reporting / coding artifact 5Lab value / disease marker 2Not in label — unassessed 21
What the badges mean
- 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.
- 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 flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 21 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 |
|---|---|---|---|---|---|---|
| Abnormal behaviour | 399 | 84.0 76.7–91.9ROR 99.5 · χ² 32,352 / p <1e-300 | 82.8 EB05 76.2 · IC025 +6.1 3/3 methods agree | Not in label — unassessed | serious PRR 99.9 · ♀ 28% (drug 52%) | no trial data cached |
| Drug exposure during pregnancy | 244 | 59.2 52.5–66.7ROR 65.4 · χ² 13,820 / p <1e-300 | 58.5 EB05 52.6 · IC025 +5.5 3/3 methods agree | Reporting / coding artifact | serious PRR 4.9 · ♀ 98% (drug 52%) | no trial data cached |
| Hypothermia | 44 | 36.2 27.0–48.5ROR 36.8 · χ² 1,465 / p <1e-300 | 35.5 EB05 27.6 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious PRR 32.5 | no trial data cached |
| Delirium | 115 | 27.7 23.2–33.1ROR 29.0 · χ² 2,930 / p <1e-300 | 27.5 EB05 23.6 · IC025 +4.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 25.6 | no trial data cached |
| Altered state of consciousness | 56 | 21.6 16.7–28.0ROR 22.1 · χ² 1,080 / p 3e-237 | 21.4 EB05 17.1 · IC025 +3.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.2 | no trial data cached |
| Hallucination, auditory | 35 | 18.3 13.2–25.4ROR 18.6 · χ² 555 / p 6e-123 | 18.1 EB05 13.5 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious PRR 19.2 · 94% clinician | no trial data cached |
| Hallucination (hallucinations) | 159 | 17.7 15.2–20.5ROR 18.8 · χ² 2,485 / p <1e-300 | 17.6 EB05 15.4 · IC025 +3.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 19.8 | no trial data cached |
| Acute respiratory distress syndrome | 34 | 16.0 11.5–22.3ROR 16.2 · χ² 463 / p 7e-103 | 15.7 EB05 11.6 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious PRR 14.6 · 100% clinician | no trial data cached |
| Overdose | 395 | 15.2 13.9–16.6ROR 17.8 · χ² 5,261 / p <1e-300 | 15.1 EB05 13.9 · IC025 +3.7 3/3 methods agree | Reporting / coding artifact | serious PRR 0.2 | no trial data cached |
| Hallucination, visual | 30 | 11.9 8.3–17.0ROR 12.0 · χ² 288 / p 6e-65 | 11.3 EB05 8.1 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 12.4 · ♀ 30% (drug 52%) | no trial data cached |
| Depressed level of consciousness | 56 | 11.8 9.1–15.3ROR 12.0 · χ² 543 / p 2e-120 | 11.5 EB05 9.1 · IC025 +3.0 3/3 methods agree | Not in label — unassessed | serious PRR 11.2 | no trial data cached |
| Erythema multiforme | 12 | 10.7 6.1–18.8ROR 10.8 · χ² 96 / p 6e-23 | 9.0 EB05 5.0 · IC025 +2.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 10.1 | no trial data cached |
| Restlessness | 47 | 10.7 8.0–14.2ROR 10.8 · χ² 402 / p 9e-90 | 10.3 EB05 7.9 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious PRR 13.4 · ♀ 28% (drug 52%) · 96% clinician | no trial data cached |
| Cholestasis (bile flow blockage) | 22 | 9.6 6.3–14.5ROR 9.7 · χ² 161 / p 4e-37 | 8.6 EB05 5.8 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 8.8 · 90% clinician | no trial data cached |
| Multi-organ failure | 20 | 9.5 6.1–14.7ROR 9.5 · χ² 143 / p 3e-33 | 8.4 EB05 5.5 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 8.6 | no trial data cached |
| Aggression | 57 | 9.5 7.3–12.2ROR 9.6 · χ² 423 / p 3e-94 | 9.1 EB05 7.2 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 10.4 · ♀ 18% (drug 52%) | no trial data cached |
| Body temperature decreased | 11 | 9.2 5.1–16.6ROR 9.2 · χ² 72 / p 8e-18 | 7.4 EB05 4.2 · IC025 +1.7 3/3 methods agree | Lab value / disease marker | serious PRR 8.5 | no trial data cached |
| Bronchospasm (airway tightening) | 15 | 8.7 5.3–14.4ROR 8.8 · χ² 95 / p 1e-22 | 7.4 EB05 4.6 · IC025 +1.9 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 6.4 | no trial data cached |
| Crying | 31 | 7.1 5.0–10.0ROR 7.1 · χ² 156 / p 5e-36 | 6.5 EB05 4.7 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 10.2 | no trial data cached |
| Encephalopathy | 20 | 6.8 4.4–10.5ROR 6.8 · χ² 93 / p 3e-22 | 6.0 EB05 4.1 · IC025 +1.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial data cached |
| Loss of consciousness | 104 | 6.7 5.6–8.1ROR 7.0 · χ² 506 / p 3e-112 | 6.6 EB05 5.6 · IC025 +2.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 6.3 | no trial data cached |
| Pallor | 22 | 6.7 4.4–10.2ROR 6.8 · χ² 101 / p 4e-24 | 6.0 EB05 4.1 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 8.0 · 91% clinician | no trial data cached |
| Body temperature increased | 16 | 6.5 4.0–10.6ROR 6.5 · χ² 69 / p 5e-17 | 5.6 EB05 3.6 · IC025 +1.6 3/3 methods agree | Lab value / disease marker | serious PRR 7.3 | no trial data cached |
| Convulsion (seizure) | 45 | 6.4 4.8–8.6ROR 6.5 · χ² 202 / p 3e-46 | 6.1 EB05 4.7 · IC025 +2.1 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.8 | no trial data cached |
| Fear | 21 | 6.4 4.2–9.9ROR 6.5 · χ² 91 / p 6e-22 | 5.7 EB05 3.9 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 8.0 | no trial data cached |
| Shock | 17 | 6.2 3.9–9.9ROR 6.2 · χ² 69 / p 5e-17 | 5.4 EB05 3.5 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 5.7 | no trial data cached |
| Hepatic failure | 22 | 6.1 4.0–9.2ROR 6.1 · χ² 88 / p 4e-21 | 5.4 EB05 3.8 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| Speech disorder | 38 | 6.0 4.4–8.3ROR 6.1 · χ² 155 / p 8e-36 | 5.6 EB05 4.3 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 7.2 · ♀ 27% (drug 52%) | no trial data cached |
| No adverse event | 117 | 5.5 4.6–6.5ROR 5.7 · χ² 428 / p 3e-95 | 5.4 EB05 4.6 · IC025 +2.1 3/3 methods agree | Reporting / coding artifact | – | no trial data cached |
| Agitation | 48 | 5.4 4.1–7.2ROR 5.5 · χ² 169 / p 6e-39 | 5.2 EB05 4.0 · IC025 +1.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial data cached |
| Respiratory disorder | 19 | 5.3 3.4–8.2ROR 5.3 · χ² 61 / p 2e-15 | 4.7 EB05 3.2 · IC025 +1.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.6 | no trial data cached |
| Nightmare | 22 | 5.3 3.5–8.0ROR 5.3 · χ² 72 / p 1e-17 | 4.8 EB05 3.3 · IC025 +1.5 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.8 · 91% clinician | no trial data cached |
| Amnesia (memory loss) | 40 | 5.1 3.7–6.9ROR 5.2 · χ² 128 / p 7e-30 | 4.8 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · ♀ 18% (drug 52%) · 95% clinician | no trial data cached |
| Drug eruption | 10 | 4.7 2.5–8.8ROR 4.7 · χ² 26 / p 2e-7 | 4.0 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 4.9 | no trial data cached |
| Accidental overdose | 20 | 4.5 2.9–7.0ROR 4.6 · χ² 52 / p 3e-13 | 4.1 EB05 2.8 · IC025 +1.3 3/3 methods agree | Reporting / coding artifact | serious PRR 1.0 | no trial data cached |
| Anaphylactic shock | 13 | 4.2 2.5–7.3ROR 4.2 · χ² 29 / p 4e-8 | 3.7 EB05 2.3 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 3.9 | no trial data cached |
| Haemoptysis | 14 | 4.2 2.5–7.0ROR 4.2 · χ² 31 / p 2e-8 | 3.7 EB05 2.4 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 4.3 | no trial data cached |
| Incorrect route of drug administration | 18 | 4.1 2.6–6.5ROR 4.1 · χ² 40 / p 2e-10 | 3.8 EB05 2.5 · IC025 +1.1 3/3 methods agree | Reporting / coding artifact | serious PRR 3.1 | no trial data cached |
| Stevens-johnson syndrome (severe blistering skin reaction) | 11 | 4.1 2.3–7.4ROR 4.1 · χ² 23 / p 9e-7 | 3.6 EB05 2.2 · IC025 +0.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 3.8 | no trial data cached |
| Unresponsive to stimuli | 12 | 3.9 2.2–6.8ROR 3.9 · χ² 23 / p 9e-7 | 3.4 EB05 2.1 · IC025 +0.8 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
Trial evidence (ClinicalTrials.gov)
Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).
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 |
|---|---|---|---|---|---|---|
| Abnormal behaviour | 399 | 84.0 76.7–91.9ROR 99.5 · χ² 32,352 / p <1e-300 | 82.8 EB05 76.2 · IC025 +6.1 3/3 methods agree | Not in label — unassessed | serious PRR 99.9 · ♀ 28% (drug 52%) | no trial data cached |
| Overdose | 395 | 15.2 13.9–16.6ROR 17.8 · χ² 5,261 / p <1e-300 | 15.1 EB05 13.9 · IC025 +3.7 3/3 methods agree | Reporting / coding artifact | serious PRR 0.2 | no trial data cached |
| Drug exposure during pregnancy | 244 | 59.2 52.5–66.7ROR 65.4 · χ² 13,820 / p <1e-300 | 58.5 EB05 52.6 · IC025 +5.5 3/3 methods agree | Reporting / coding artifact | serious PRR 4.9 · ♀ 98% (drug 52%) | no trial data cached |
| Hallucination (hallucinations) | 159 | 17.7 15.2–20.5ROR 18.8 · χ² 2,485 / p <1e-300 | 17.6 EB05 15.4 · IC025 +3.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 19.8 | no trial data cached |
| No adverse event | 117 | 5.5 4.6–6.5ROR 5.7 · χ² 428 / p 3e-95 | 5.4 EB05 4.6 · IC025 +2.1 3/3 methods agree | Reporting / coding artifact | – | no trial data cached |
| Delirium | 115 | 27.7 23.2–33.1ROR 29.0 · χ² 2,930 / p <1e-300 | 27.5 EB05 23.6 · IC025 +4.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 25.6 | no trial data cached |
| Loss of consciousness | 104 | 6.7 5.6–8.1ROR 7.0 · χ² 506 / p 3e-112 | 6.6 EB05 5.6 · IC025 +2.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 6.3 | no trial data cached |
| Aggression | 57 | 9.5 7.3–12.2ROR 9.6 · χ² 423 / p 3e-94 | 9.1 EB05 7.2 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 10.4 · ♀ 18% (drug 52%) | no trial data cached |
| Depressed level of consciousness | 56 | 11.8 9.1–15.3ROR 12.0 · χ² 543 / p 2e-120 | 11.5 EB05 9.1 · IC025 +3.0 3/3 methods agree | Not in label — unassessed | serious PRR 11.2 | no trial data cached |
| Altered state of consciousness | 56 | 21.6 16.7–28.0ROR 22.1 · χ² 1,080 / p 3e-237 | 21.4 EB05 17.1 · IC025 +3.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.2 | no trial data cached |
| Agitation | 48 | 5.4 4.1–7.2ROR 5.5 · χ² 169 / p 6e-39 | 5.2 EB05 4.0 · IC025 +1.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial data cached |
| Restlessness | 47 | 10.7 8.0–14.2ROR 10.8 · χ² 402 / p 9e-90 | 10.3 EB05 7.9 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious PRR 13.4 · ♀ 28% (drug 52%) · 96% clinician | no trial data cached |
| Convulsion (seizure) | 45 | 6.4 4.8–8.6ROR 6.5 · χ² 202 / p 3e-46 | 6.1 EB05 4.7 · IC025 +2.1 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.8 | no trial data cached |
| Hypothermia | 44 | 36.2 27.0–48.5ROR 36.8 · χ² 1,465 / p <1e-300 | 35.5 EB05 27.6 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious PRR 32.5 | no trial data cached |
| Amnesia (memory loss) | 40 | 5.1 3.7–6.9ROR 5.2 · χ² 128 / p 7e-30 | 4.8 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · ♀ 18% (drug 52%) · 95% clinician | no trial data cached |
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.
- Abnormal behaviour — n=399, PRR 84.0
- Hypothermia — n=44, PRR 36.2
- Hallucination, auditory — n=35, PRR 18.3
- Acute respiratory distress syndrome — n=34, PRR 16.0
- Hallucination, visual — n=30, PRR 11.9
- Depressed level of consciousness — n=56, PRR 11.8
- Restlessness — n=47, PRR 10.7
- Cholestasis — n=22, PRR 9.6
- Multi-organ failure — n=20, PRR 9.5
- Aggression — n=57, PRR 9.5
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 Zanamivir?
In FDA FAERS, the most frequently co-reported reaction terms for Zanamivir are abnormal behaviour, hallucination, delirium, loss of consciousness, aggression, depressed level of consciousness. 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 Zanamivir have an FDA boxed warning?
No. The FDA label retrieved for Zanamivir has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Zanamivir 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 b4e68930-4e6d-4d27-b1f0-abf60d12e28d, effective 20260723; matched on
openfda.generic_name.exact:"ZANAMIVIR") - 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, 61 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
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.