Pharmacologic class (EPC) · 2 drug pages

Vitamin K antagonist: adverse event reports filed with FDA

42,833 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.

42,833
reports across the class: 0.2% of all reports; 842
reports, 12 months to June 2026: 1,153 in the 12 months before; 88.7%
marked serious by the reporter: 57.4% across all reports; 2
drugs with a page: brand and generic names counted separately

Vitamin K antagonist 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 42,833 adverse event reports received by FDA, 0.2% of the database, from January 2004 to June 2026.

842 reports arrived in the 12 months to June 2026, down 27% from 1,153 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 88.7% of the class's reports are marked serious, 12.8% record death among the outcomes and 52.5% record hospitalisation, as reported.

Across the class the reactions recorded most often are international normalised ratio increased (20.7%), drug interaction (12.1%) and haemorrhage (7.9%). 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
Warfarin	generic	23,392	613	91.8%	International normalised ratio increased
Warfarin sodium	generic	19,441	229	84.9%	International normalised ratio increased

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

International normalised ratio increasedblood clotting slower than intended (raised INR)20.7%8,875
Drug interactionan interaction between medicines12.1%5,200
Haemorrhagebleeding7.9%3,389
Gastrointestinal haemorrhagebleeding in the stomach or bowel5.9%2,535
Anaemialow red blood cells5.2%2,232
Drug ineffectivethe medicine did not work as expected3.9%1,670
Haemoglobin decreasedlow haemoglobin3.9%1,667
Falla fall3.5%1,520
Dyspnoeashortness of breath3.5%1,484
Epistaxisnosebleed3.4%1,458
Contusiona bruise3.4%1,451
Haematomaa collection of blood under the skin or in tissue3.1%1,326
Haematuriablood in the urine2.9%1,232
Haemorrhage intracranial2.8%1,180
Nauseafeeling sick2.8%1,180
Cerebral haemorrhage2.7%1,143
Rectal haemorrhage2.7%1,140
Astheniaweakness or lack of energy2.6%1,114
Off label useused for a purpose or in a way not on the label2.6%1,095
International normalised ratio decreasedblood clotting faster than intended (low INR)2.5%1,077
Hypotensionlow blood pressure2.5%1,068
Melaenablack tarry stools2.5%1,061
International normalised ratio abnormal2.5%1,059
Gastric haemorrhage2.5%1,054
Fatiguetiredness2.4%1,045

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

Death12.8%5,487

Life-threatening9.9%4,223

Hospitalisation (initial or prolonged)52.5%22,494

Disability2.5%1,076

Congenital anomaly0.4%192

Other serious47.5%20,337

Not serious11.3%4,856

Patient age

Under 20.1%57

2 to 110.4%163

12 to 170.5%196

18 to 445.8%2,498

45 to 6418.9%8,093

65 to 7418.6%7,988

75 and over29%12,424

Age not given26.6%11,414

Who reported

Physician18.2%7,782

Pharmacist25.5%10,938

Other health professional32.6%13,945

Lawyer0.1%31

Consumer or non-health professional18.7%8,023

Not given4.9%2,114

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 Vitamin K antagonist reports

Which drugs are in the Vitamin K antagonist class on this site?

Warfarin and Warfarin sodium. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

42,833 reports through June 2026, 842 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?

international normalised ratio increased (20.7%), drug interaction (12.1%), haemorrhage (7.9%), gastrointestinal haemorrhage (5.9%) and anaemia (5.2%).

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.