Warfarin Side Effects

Medically reviewed by Drugs.com. Last updated on Mar 24, 2023.

Applies to warfarin: oral tablet.

Other dosage forms:

• intravenous powder for solution

Important warnings This medicine can cause some serious health issues

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 warfarin

Along with its needed effects, warfarin 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 side effects

• bleeding gums
• blood in the urine
• bloody stools
• blurred vision
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• chest pain or discomfort
• confusion
• coughing up blood
• difficulty with breathing or swallowing
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• excessive bruising
• headache
• increased menstrual flow or vaginal bleeding
• nosebleeds
• paralysis
• peeling of the skin
• prolonged bleeding from cuts
• red or black, tarry stools
• red or dark brown urine
• stomach pain with cramping
• sweating
• unexplained swelling
• unusual tiredness or weakness

Rare side effects

• arm, back, or jaw pain
• blue-green to black skin discoloration
• blue or purple toes
• change in consciousness
• chest tightness or heaviness
• chills
• clay-colored stools
• diarrhea
• dizziness
• fainting or loss of consciousness
• fast or irregular breathing
• fast or irregular heartbeat
• fever
• itching or skin rash
• light-colored stools
• loss of appetite
• nausea and vomiting
• pain in the toes
• pain, redness, or sloughing of the skin
• pale skin
• purplish red, net-like, blotchy spots on the skin
• skin blisters
• small red or purple spots on the skin
• stomach pain
• swelling of the eyes or eyelids
• troubled breathing with exertion
• unpleasant breath odor
• unusual bleeding or bruising
• upper right stomach pain
• vomiting of blood
• yellow eyes and skin

Other side effects of warfarin

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 side effects

• joint pain
• muscle pain

Rare side effects

• bloated
• change in taste, or bad, unusual, or unpleasant (after) taste
• cold intolerance
• excess air or gas in the stomach or intestines
• full feeling
• general feeling of discomfort or illness
• hair loss or thinning of the hair
• hives or welts
• lack or loss of strength
• pain
• passing gas
• red, sore, or itching skin
• sores, welting, or blisters
• unusual drowsiness, dullness, or feeling of sluggishness

For healthcare professionals

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

General adverse events

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

Cardiovascular

• 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]

Gastrointestinal

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

Dermatologic

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

Musculoskeletal

• Frequency not reported: Tissue necrosis, chills^[Ref]

Metabolic

• Frequency not reported: Calciphylaxis, edema^[Ref]

Respiratory

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

Genitourinary

• Frequency not reported: Hematuria^[Ref]

Hematologic

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

Hepatic

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

Immunologic

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

Other

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

Frequently asked questions

• What is the antidote for warfarin?
• Is warfarin used as rat poison?
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• Why does warfarin cause purple toe syndrome?
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• Why are Warfarin tablets color-coded?
• Is your blood really thinner with warfarin?

Further information

Warfarin side effects can vary depending on the individual. 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.

Medical Disclaimer