Pharmacologic class (EPC) · 2 drug pages

Interferon alpha: adverse event reports filed with FDA

43,695 reports list a drug in this class as a suspect or interacting product, 2004–2026.

Read first · FDA's statement on these data

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product. openFDA, FDA

FDA adds: "There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event." The information in these reports "cannot be used to estimate the incidence of these events."

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

43,695
reports across the class: 0.2% of all reports; 180
reports, 12 months to June 2026: 145 in the 12 months before; 45.4%
marked serious by the reporter: 57.4% across all reports; 2
drugs with a page: brand and generic names counted separately

Interferon alpha is a pharmacologic class (an FDA Established Pharmacologic Class) with 2 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 43,695 adverse event reports received by FDA, 0.2% of the database, from January 2004 to June 2026.

180 reports arrived in the 12 months to June 2026, up 24% from 145 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 45.4% of the class's reports are marked serious, 3.7% record death among the outcomes and 18% record hospitalisation, as reported.

Across the class the reactions recorded most often are fatigue (16.5%), nausea (12.9%) and anaemia (11.9%). The class median share shown beside each term is the middle value across the member drugs; it is the comparison used on every drug page in this class.

The members table is 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."

Drugs in the class

Drug	Name type	Reports	Latest 12 months	Marked serious	Top term recorded
PegasysPeginterferon alfa-2a	brand	40,361	158	41.9%	Fatigue
Peginterferon alfa-2a	generic	3,334	22	88.8%	Anaemia

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."

Reports by month, five years

FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

Reactions recorded across the class

share of class reports recording the termmedian drug in the class

Fatiguetiredness16.5%7,205
Nauseafeeling sick12.9%5,638
Anaemialow red blood cells11.9%5,216
White blood cell count decreasedlow white cell count8.5%3,735
Headachehead pain8.5%3,710
Rashskin rash8.3%3,646
Pruritusitching7.3%3,177
Pyrexiafever6.8%2,972
Insomniadifficulty sleeping6%2,643
Vomitingbeing sick6%2,618
Diarrhoealoose or frequent stools5.9%2,568
Astheniaweakness or lack of energy5.8%2,531
Dyspnoeashortness of breath5.6%2,444
Decreased appetitereduced appetite5.6%2,427
Weight decreasedweight loss5.3%2,327
Platelet count decreasedlow platelet count5.2%2,291
Influenza like illnessflu-like symptoms5.1%2,227
Depressionlow mood5.1%2,209
Painpain, site not specified5%2,183
Dizzinesslight-headedness or unsteadiness4.8%2,098
Chillschills or shivering4.2%1,856
Haemoglobin decreasedlow haemoglobin4%1,736
Alopeciahair loss3.3%1,450
Drug ineffectivethe medicine did not work as expected3.2%1,399
Malaisegeneral feeling of being unwell3.2%1,385

Solid bar: share of all class reports. Hollow bar: the median share across the 2 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death3.7%1,595

Life-threatening1.9%836

Hospitalisation (initial or prolonged)18%7,882

Disability1.4%613

Congenital anomaly0.2%73

Other serious28.3%12,362

Not serious54.6%23,836

Patient age

Under 20.1%36

2 to 110.1%51

12 to 170.1%52

18 to 4410.2%4,443

45 to 6434.7%15,163

65 to 744.2%1,825

75 and over0.6%248

Age not given50.1%21,877

Who reported

Physician20.1%8,782

Pharmacist3.6%1,574

Other health professional14.2%6,185

Lawyer0.1%28

Consumer or non-health professional59.7%26,107

Not given2.3%1,019

Grey bar: all 20,646,523 reports in the database. Outcome flags are as the reporter set them and are not verified by FDA.

Questions about Interferon alpha reports

Which drugs are in the Interferon alpha class on this site?

Pegasys and Peginterferon alfa-2a. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

43,695 reports through June 2026, 180 of them in the latest 12 months. A report listing two drugs of the class counts once for each.

What reactions are recorded most often?

fatigue (16.5%), nausea (12.9%), anaemia (11.9%), white blood cell count decreased (8.5%) and headache (8.5%).

Can the members table be used to rank the drugs?

No. 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." Drugs differ in how many people take them, in the conditions they treat, in time on the market and in how diligently reports are collected.

How do I report an adverse event?

Through FDA MedWatch (Form FDA 3500, or 1-800-FDA-1088) or to the manufacturer. 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 class is the Established Pharmacologic Class most often attached to a drug's reports by openFDA's label harmonisation, or from the NDC Directory where reports carry none. 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.