Drugs › Neuraminidase inhibitor
Brand name · Zanamivir
Relenza: adverse event reports filed with FDA
2,073 reports list it as a suspect or interacting product, 2004–2023. Class: Neuraminidase inhibitor. Also reported as Relenza Inhaler.
- 2,073
- reports as suspect product
- 0% of all reports · about 93 a year
- 0
- reports, 12 months to June 2026
- 0 in the 12 months before
- 56.4%
- marked serious by the reporter
- 60.6% across the class
- 2.5%
- record death among outcomes, as reported
- 51 reports · not verified by FDA
2,073 adverse event reports received by FDA list the brand name Relenza (zanamivir) as a suspect or interacting product, from February 2004 to November 2023. A further 61 reports list it only as a concomitant medication, and those are not counted in the figures on this page.
In the 12 months to June 2026, 0 reports listed it, and none in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 93 reports a year and 0% of the 20,646,523 reports in the database, and 10.2% of the reports for the neuraminidase inhibitor class. How many people take it is not in the data, so a count is not a rate of occurrence.
The MedDRA terms listed most often are overdose (19%), abnormal behaviour (18.7%) and drug exposure during pregnancy (11.3%). A report can list several reactions, so shares add to more than 100%; 268 different terms appear across these reports. Overdose is recorded in 19% of these reports, a larger share than in the median neuraminidase inhibitor drug (1.2%).
56.4% of the reports are marked serious by the reporter (60.6% across the class); 2.5% record death among the outcomes and 10.4% record hospitalisation, as reported. 38.2% of the reports came from physicians, and the largest patient age group is 2 to 11 (22.1%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
Reports by month, five years
Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.
By year received
Reactions recorded in the reports
share of Relenza reports recording the termmedian drug in neuraminidase inhibitor
- Overdosea dose above the recommended amount19%393
- Abnormal behaviourunusual behaviour18.7%387
- Drug exposure during pregnancythe medicine was taken during pregnancy11.3%235
- Hallucinationseeing or hearing things that are not there7.3%152
- Drug exposure via breast milk5.9%123
- No adverse eventno adverse event was reported5.5%114
- Deliriumsudden confusion5.3%110
- Loss of consciousnesspassing out4.6%95
- Pyrexiafever3.3%69
- Aggressionaggressive behaviour2.6%54
- Falla fall2.4%49
- Restlessnessrestlessness2.2%46
- Dyspnoeashortness of breath2.1%44
- Agitationrestlessness2.1%43
- Convulsion2.1%43
- Vomitingbeing sick2.1%43
- Nauseafeeling sick2%41
- Hypothermia1.9%40
- Feeling abnormalfeeling odd or not right1.8%37
- Amnesiamemory loss1.7%35
- Hallucination, auditory1.5%32
- Headachehead pain1.5%32
- Speech disordera speech problem1.5%32
- Delivery1.5%31
- Dizzinesslight-headedness or unsteadiness1.5%31
- Memory impairmentmemory problems1.4%30
- Asthmaasthma1.4%28
- Cryingcrying1.4%28
Top 30 of 268 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 4 drugs in the neuraminidase inhibitor class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Outcomes recorded
Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 20,262 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."
Patients and reporters
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 5.3% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Influenza | 1,153 | 55.6% |
| Antiviral prophylaxis | 51 | 2.5% |
| H1n1 influenza | 36 | 1.7% |
| Prophylaxis | 11 | 0.5% |
| Drug exposure via breast milk | 5 | 0.2% |
| Influenza like illness | 3 | 0.1% |
The indication field is filled in by the reporter and is often blank; shares are of all 2,073 reports.
In context
| Measure | Relenza | Neuraminidase inhibitor | All reports |
|---|---|---|---|
| Reports as suspect product | 2,073 | 20,262 | 20,646,523 |
| Share of that pool | — | 10.2% | 0% |
| Reports, latest 12 months | 0 | — | 1,332,454 |
| Marked serious | 56.4% | 60.6% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 25 | 102 | 91 |
| Hospitalisation recorded, per 1,000 reports | 104 | 200 | 213 |
| Consumer-filed share | 27.5% | 32.8% | 45.8% |
| Top term, share of reports | Overdose 19% | median 1.2% | 1% |
Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Other drugs in the neuraminidase inhibitor class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Tamiflu | brand | 13,223 | 190 | 57.2% |
| Oseltamivir | generic | 3,897 | 211 | 72.8% |
| Oseltamivir phosphate | generic | 1,069 | 120 | 66.9% |
Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.
Questions about Relenza reports
How many adverse event reports has FDA received for Relenza?
2,073 reports list Relenza as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 0 of them arrived in the latest 12 months. Another 61 list it only as a concomitant medication.
What reactions are recorded in Relenza reports?
overdose (19%), abnormal behaviour (18.7%), drug exposure during pregnancy (11.3%), hallucination (7.3%) and drug exposure via breast milk (5.9%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Relenza was responsible.
How serious are the reports?
56.4% are marked serious by the reporter. Among the outcomes recorded, 2.5% of reports include death and 10.4% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
physician (38.2%), pharmacist (32.1%) and consumer or non-health professional (27.5%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Relenza rising?
0 reports in the 12 months to June 2026, and none in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Relenza was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Relenza?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. See the guide on how to report.
Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Relenza as a suspect or interacting product; reports listing it only as a concomitant medication (61) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.
Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.