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Coumadin Side Effects

Generic name: warfarin

Medically reviewed by Last updated on Mar 24, 2023.

Note: This document contains side effect information about warfarin. Some dosage forms listed on this page may not apply to the brand name Coumadin.

Applies to warfarin: oral tablet. Other dosage forms:


Oral route (Tablet)

Warfarin can cause major or fatal bleeding. Regular monitoring of INR should be performed on all treated patients. Drugs, dietary changes, and other factors affect INR levels achieved with warfarin sodium therapy. Instruct patients about prevention measures to minimize risk of bleeding and to report signs and symptoms of bleeding.

Serious side effects of Coumadin

Along with its needed effects, warfarin (the active ingredient contained in Coumadin) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking warfarin:

Less common


Other side effects of Coumadin

Some side effects of warfarin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common


For Healthcare Professionals

Applies to warfarin: compounding powder, intravenous powder for injection, oral tablet.


The most common adverse reactions were fatal and nonfatal hemorrhage from any tissue or organ.[Ref]


Frequency not reported: Hemorrhage, purple toes syndrome, infarction, systemic cholesterol microembolization, vasculitis, systemic atheroemboli[Ref]

Nervous system

Frequency not reported: Cerebral hemorrhage, cerebral subdural hematoma, lethargy, headache, dizziness, taste perversion, paresthesia[Ref]


Frequency not reported: Gastrointestinal hemorrhage, rectal hemorrhage, hematemesis, pancreatitis, diarrhea, nausea, vomiting, melena, abdominal pain, cramping, flatulence, bloating[Ref]


Frequency not reported: Rash, alopecia, purpura, erythematous swollen skin patches, ecchymosis, skin necrosis, dermatitis, bullous eruptions, urticaria, pruritus[Ref]


Frequency not reported: Tissue necrosis, chills[Ref]


Frequency not reported: Calciphylaxis, edema[Ref]


Frequency not reported: Hemothorax, epistaxis, tracheal or tracheobronchial calcification[Ref]


Frequency not reported: Hematuria[Ref]


Frequency not reported: Unexplained decrease in hematocrit, hemoglobin decreased[Ref]


Frequency not reported: Jaundice, hepatic dysfunction, hepatitis, cholestatic hepatic injury, liver enzymes elevated[Ref]


Frequency not reported: Hypersensitivity, allergic reactions, anaphylactic reactions[Ref]


Frequency not reported: Fever, fatigue, malaise, asthenia, pain, cold intolerance, feeling cold[Ref]

Frequently asked questions


1. Product Information. Coumadin (warfarin). DuPont Pharmaceuticals. 2001.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Cerner Multum, Inc. Australian Product Information.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.