- What is warfarin, and how does it work (mechanism of action)?
- What brand names are available for warfarin?
- Is warfarin available as a generic drug?
- Do I need a prescription for warfarin?
- What are the uses for warfarin?
- What are the side effects of warfarin?
- What is the dosage for warfarin?
- Which drugs or supplements interact with warfarin?
- Is warfarin safe to take if I'm pregnant or breastfeeding?
- What else should I know about warfarin?
What is warfarin, and how does it work (mechanism of action)?
- Warfarin is an oral anticoagulant, a drug that inhibits the clotting of blood. It prevents the formation of blood clots by reducing the production of factors by the liver that promote clotting, factors II, VII, IX, and X, and the anticoagulant proteins C and S. The production of these factors by the liver are dependent on adequate amounts of vitamin K. Warfarin reduces the production of the factors because it antagonizes vitamin K. Blood clots can occur in the veins of the lower extremities (deep venous thrombosis [DVT]), often after periods of immobility. These clots can break off and become lodged in the blood vessels of the lung (pulmonary embolism), causing shortness of breath, chest pain, and even life-threatening shock. Blood clots can also occur in the atria of the heart during atrial fibrillation and around artificial heart valves. These clots also can break off and obstruct blood vessels in the brain, causing an embolic stroke with paralysis. Warfarin is important in preventing the formation of blood clots, preventing extension of clots already formed, and minimizing the risk of embolization of blood clots to other vital organs such as the lungs and brain.
- The FDA approved warfarin in June 1954.
What are the uses for warfarin?
- Warfarin is used in treating patients with deep vein thrombosis (DVT) to prevent extension of the clot, and to reduce the risk of pulmonary embolism.
- Patients with pulmonary embolism are treated with warfarin to prevent further emboli.
- Warfarin also is used in patients with atrial fibrillation or artificial heart valves to reduce the risk of strokes, and after a heart attack.
- It also is helpful in preventing blood clots from forming in certain orthopedic surgeries such as knee or hip replacements.
- Warfarin is used in preventing closure of coronary artery stents due to clotting.

QUESTION
In the U.S., 1 in every 4 deaths is caused by heart disease. See AnswerWhat are the side effects of warfarin?
The two most serious side effects of warfarin are:
- Bleeding
- Necrosis (gangrene) of the skin
Bleeding can occur in any organ or tissue. Bleeding around the brain can cause severe headache and paralysis. Bleeding in the joints can cause joint pain and swelling. Bleeding in the stomach or intestines can cause weakness, fainting spells, black tarry stools, vomiting of blood, or coffee ground material. Bleeding in the kidneys can cause back pain and blood in urine.
Other side effects include:
Signs of overdose include bleeding gums, bruising, nosebleeds, heavy menstrual bleeding, and prolonged bleeding from cuts.
What is the dosage for warfarin?
- Warfarin may be taken with or without food.
- Since warfarin is metabolized (inactivated) by the liver and then excreted by the kidneys, dosages need to be lowered in patients with liver and kidney dysfunction.
- Frequent blood tests (INR test) are performed to measure the effect of warfarin and to adjust dosing.
- There are published INR ranges for the various uses of warfarin.
- Treatment usually is started at 2 to 5 mg once daily and the dose is adjusted based in INR tests.
- Patients typically require 2 to 10 mg of warfarin daily.
Which drugs or supplements interact with warfarin?
- Many drugs, both prescription and nonprescription (OTC), can affect the anticoagulant action of warfarin or increase the risk of bleeding. Patients on warfarin should regularly consult their doctor before instituting any medications on their own.
- It also is advisable for patients on warfarin to carry identification such as bracelets to alert other health professionals to the presence of anticoagulation.
- A few examples of drugs that interact with warfarin are:
- Drugs that increase the effect of warfarin by reducing the breakdown of warfarin include amiodarone (Cordarone), trimethoprim/sulfamethoxazole (Bactrim), fluconazole (Diflucan), itraconazole (Sporanox), fluvastatin, fluvoxamine, metronidazole miconazole, voriconazole (Vfend), zafirlukast (Accolate), ciprofloxacin (Cipro), cimetidine, atorvastatin (Lipitor), clarithromycin (Biaxin), fluoxetine (Prozac), indinavir (Crixivan), and ritonavir (Norvir).
- Drugs that may reduce the effect of warfarin by increasing its breakdown include St. John's wort, carbamazepine (Tegretol, Tegretol XR, Equetro, Carbatrol), rifampin, bosentan (Tracleer), and prednisone.
- Bleeding is increased by other anticoagulants such as heparin, argatroban (Acova), dabigatran (Pradaxa), and others; antiplatelet drugs such as aspirin and other nonsteroidal anti-inflammatory drugs (for example, ibuprofen [Motrin], naproxen [Alleve]), clopidogrel (Plavix), and prasugrel (Effient); serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac) and paroxetine (Paxil). Garlic and ginkgo also increase the risk of bleeding because they cause bleeding when taken alone.
- Foods with high vitamin K content (for example, green leafy vegetables) reduce the effect of warfarin. Maintenance of a consistent intake of vitamin K containing foods is important to avoid fluctuations in the effect of warfarin.
Is warfarin safe to take if I'm pregnant or breastfeeding?
- Warfarin should be avoided by pregnant women or women who may become pregnant. Birth defects and fetal bleeding have been reported.
- Available evidence suggests that warfarin is not secreted in breast milk.
What else should I know about warfarin?
What preparations of warfarin are available?
- Tablets: 1, 2, 2.5, 3, 4, 5, 6, 5, 7.5 and 10 mg.
- Powder for Injection: 5 mg/vial
How should I keep warfarin stored?
Warfarin should be stored at room temperature, 59 F to 86 F (15 C to 30 C), in tight, light resistant container.
Subscribe to MedicineNet's Heart Health Newsletter
By clicking "Submit," I agree to the MedicineNet Terms and Conditions and Privacy Policy. I also agree to receive emails from MedicineNet and I understand that I may opt out of MedicineNet subscriptions at any time.
Summary
Warfarin (Coumadin, Jantoven) is an anticoagulant drug that inhibits the blood from clotting, thus preventing blood clots. It is prescribed for the treatment of patients with deep vein thrombosis, the reduction of pulmonary embolism, and in patients with atrial fibrillation to reduce the risk of strokes and heart attack. Common side effects of warfarin include:
Drug interactions, and warnings and precautions, and pregnancy and breastfeeding information should be reviewed prior to taking this medication.
Multimedia: Slideshows, Images & Quizzes
-
Atrial Fibrillation: Heart Symptoms, Diagnosis, & AFib Treatment
AFib symptoms like heart racing, fluttering, and irregular heart beat may be caused by heart disease, obesity, alcohol use,...
-
Heart Healthy Diet: 25 Foods You Should Eat
What foods are heart healthy? Learn what foods help protect your cardiovascular system from heart attack, coronary heart disease,...
-
Heart Disease: Causes of a Heart Attack
Heart disease prevention includes controlling risk factors like diet, exercise, and stress. Heart disease symptoms in women may...
-
Am I Having a Heart Attack? Symptoms of Heart Disease
Heart attacks symptoms vary greatly for men and women, from anxiety and fatigue to nausea and sweating. Learn the warning signs...
-
High-Fiber Super Foods: Whole Grains, Fruits, & More
Learn about high-fiber foods. From fresh fruits to whole grains, these fiber-rich foods can lower cholesterol, prevent...
-
A Visual Guide to Deep Vein Thrombosis (DVT)
Deep vein thrombosis (DVT) is a dangerous and sometimes fatal blood clot that occurs deep within the lower leg or thigh....
-
Heart Disease: Symptoms, Signs, and Causes
What is heart disease (coronary artery disease)? Learn about the causes of heart disease, arrhythmias and myopathy. Symptoms of...
-
How to Lower Your Cholesterol & Save Your Heart
Need to lower your cholesterol levels? Use these smart diet tips to quickly and easily lower your blood cholesterol levels....
-
Stroke Quiz: Test Your Medical IQ
Take the Stroke Quiz to learn about stroke risks, causes, treatment, and most importantly, prevention.
-
Atrial Fibrillation (A-Fib) Quiz: Test Your Medical IQ
Learn the causes, symptoms, and treatments of the common heart abnormality known as atrial fibrillation (A-fib).
-
Heart Disease Quiz: Test Your Medical IQ
Take our Heart Disease Quiz to get answers and facts about high cholesterol, atherosclerosis prevention, and the causes,...
-
Picture of Heart Detail
The heart is composed of specialized cardiac muscle, and it is four-chambered, with a right atrium and ventricle, and an...
-
Picture of Blood Clot
Blood that has been converted from a liquid to a solid state. See a picture of Blood Clot and learn more about the health topic.
-
Picture of Heart
The muscle that pumps blood received from veins into arteries throughout the body. See a picture of the Heart and learn more...
-
12 Reasons to Love the Mediterranean Diet
The Mediterranean diet is a delicious way to eat healthy. We show you how to get the most from this diet with foods like olive...
-
Food Swaps for Meals and Snacks for Heart Health in Pictures
Explore 10 food swaps for heart-wise dining. Learn what food to buy and how to cook in order to make a big difference for your...
Related Disease Conditions
-
Blood Clots (in the Leg)
Blood clots can form in the heart, legs, arteries, veins, bladder, urinary tract, and uterus. Risk factors include high blood pressure and cholesterol, diabetes, smoking, and family history. Symptoms and treatment depend on the location of the clot.
-
Heart Attack Symptoms and Early Warning Signs
Recognizing heart attack symptoms and signs can help save your life or that of someone you love. Some heart attack symptoms, including left arm pain and chest pain, are well known but other, more nonspecific symptoms may be associated with a heart attack. Nausea, vomiting, malaise, indigestion, sweating, shortness of breath, and fatigue may signal a heart attack. Heart attack symptoms and signs in women may differ from those in men.
-
How the Heart Works
The heart is a very important organ in the body. It is responsible for continuously pumping oxygen and nutrient-rich blood throughout your body to sustain life. It is a fist-sized muscle that beats (expands and contracts) 100,000 times per day, pumping a total of five or six quarts of blood each minute, or about 2,000 gallons per day.
-
Internal Bleeding
Internal bleeding is a serious consequence of trauma and can be life-threatening, requiring immediate medical attention. Learn about signs, causes, and treatment.
-
Congestive Heart Failure (CHF)
Congestive heart failure (CHF) refers to a condition in which the heart loses the ability to function properly. Heart disease, high blood pressure, diabetes, myocarditis, and cardiomyopathies are just a few potential causes of congestive heart failure. Signs and symptoms of congestive heart failure may include fatigue, breathlessness, palpitations, angina, and edema. Physical examination, patient history, blood tests, and imaging tests are used to diagnose congestive heart failure. Treatment of heart failure consists of lifestyle modification and taking medications to decrease fluid in the body and ease the strain on the heart. The prognosis of a patient with congestive heart failure depends on the stage of the heart failure and the overall condition of the individual.
-
Chest Pain
Chest pain is a common complaint by a patient in the ER. Causes of chest pain include broken or bruised ribs, pleurisy, pneumothorax, shingles, pneumonia, pulmonary embolism, angina, heart attack, costochondritis, pericarditis, aorta or aortic dissection, and reflux esophagitis. Diagnosis and treatment of chest pain depends upon the cause and clinical presentation of the patient's chest pain.
-
Arrhythmias (Abnormal Heart Rhythms)
Heart rhythm disorders vary from minor palpitations, premature atrial contractions (PACs), premature ventricular contractions (PVCs), sinus tachycardia, and sinus bradycardia, to abnormal heart rhythms such as tachycardia, ventricular fibrillation, ventricular flutter, atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), Wolf-Parkinson-White syndrome, brachycardia, or heart blocks. Treatment is dependent upon the type of heart rhythm disorder.
-
Atrial Fibrillation (AFib)
Atrial fibrillation (AF or AFib) is an abnormality in the heart rhythm, which involves irregular and often rapid beating of the heart. Symptoms may include heart palpitations, dizziness, fainting, fatigue, shortness of breath, and chest pain. Atrial fibrillation treatment may include medication or procedures like cardioversion or ablation to normalize the heart rate.
-
Stroke
A stroke is an interruption of the blood supply to part of the brain caused by either a blood clot (ischemic) or bleeding (hemorrhagic). Symptoms of a stroke may include weakness, numbness, double vision or vision loss, confusion, vertigo, difficulty speaking, or understanding speech. A physical exam, imaging tests, neurological exam, and blood tests may be used to diagnose a stroke. Treatment may include administration of clot-busting drugs, supportive care, and in some instances, neurosurgery. The risk of stroke can be reduced by controlling high blood pressure, high cholesterol, diabetes, and stopping smoking.
-
Pulmonary Embolism (Blood Clot in the Lung)
A pulmonary embolism (PE) occurs when a piece of a blood clot from deep vein thrombosis (DVT) breaks off and travels to an artery in the lung where it blocks the artery and damages the lung. The most common symptoms of a pulmonary embolism are shortness of breath, chest pain, and a rapid heart rate. Causes of pulmonary embolism include prolonged immobilization, certain medications, smoking, cancer, pregnancy, and surgery. Pulmonary embolism can cause death if not treated promptly.
-
Gangrene
Gangrene may result when blood flow to a tissue is lost or not adequate to keep the tissue alive. There are two types of gangrene: wet and dry. All cases of wet gangrene are infected by bacteria. Most cases of dry gangrene are not infected. If wet gangrene goes untreated, the patient may die of sepsis within hours or days. Dry gangrene usually doesn't cause the patient to die. Symptoms of dry gangrene include numbness, discoloration, and mummification of the affected tissue. Wet gangrene symptoms include swelling, pain, pus, bad smell, and a black appearance of the affected tissue. Treatment depends upon the type of gangrene and how much tissue is compromised by the gangrene.
-
Heart Disease
Heart disease (coronary artery disease) occurs when plaque builds up in the coronary arteries, the vessels that supply blood to the heart. Heart disease can lead to heart attack. Risk factors for heart disease include: Smoking High blood pressure High cholesterol Diabetes Family history Obesity Angina, shortness of breath, and sweating are just a few symptoms that may indicate a heart attack. Treatment of heart disease involves control of heart disease risk factors through lifestyle changes, medications, and/or stenting or bypass surgery. Heart disease can be prevented by controlling heart disease risk factors.
-
Heart Attack (Myocardial Infarction)
A heart attack occurs when a blood clot completely obstructs a coronary artery supplying blood to the heart muscle. Learn about warning signs, causes, complications, risk factors, and treatment.
-
Deep Vein Thrombosis (DVT, Blood Clot in the Legs)
Deep vein thrombosis (DVT) is a blood clot in the deep veins, and can be caused by broken bones, trauma to a limb, immobility, medications, smoking, cancer, genetic predisposition, and cancer. Symptoms and signs of a deep vein thrombosis in a leg are swelling, tenderness, redness, warmth, and pain. Treatments for DVT include medications and surgery.
-
Palpitations
Palpitations are uncomfortable sensations of the heart beating hard, rapidly, or irregularly. Some types of palpitations are benign, while others are more serious. Palpitations are diagnosed by taking the patient history and by performing an EKG or heart monitoring along with blood tests. An electrophysiology study may also be performed. Treatment of palpitations may include lifestyle changes, medication, ablation, or implantation of a pacemaker. The prognosis if palpitations depends on the underlying cause.
-
Atrial Fibrillation (AFib) Treatment Drugs
Atrial fibrillation (AFib) is a heart rhythm disorder that causes irregular and often rapid heartbeat. The medications to treat AFib include beta-blockers, blood thinners, and heart rhythm drugs. Atrial fibrillation drugs can cause serious side effects like seizures, vision changes, shortness of breath, fainting, other abnormal heart rhythms, excessive bleeding while coughing or vomiting, blood in the stool, and bleeding into the brain.
-
Peripheral Vascular Disease
Peripheral vascular disease (PVD) refers to diseases of the blood vessels (arteries and veins) located outside the heart and brain. While there are many causes of peripheral vascular disease, doctors commonly use the term peripheral vascular disease to refer to peripheral artery disease (peripheral arterial disease, PAD), a condition that develops when the arteries that supply blood to the internal organs, arms, and legs become completely or partially blocked as a result of atherosclerosis. Peripheral artery disease symptoms include intermittent leg pain while walking, leg pain at rest, numbness in the legs or feet, and poor wound healing in the legs or feet. Treatment for peripheral artery disease include lifestyle measures, medication, angioplasty, and surgery.
-
What Are the 7 More Dangerous Medicines to Mix?
Some drug interactions can have serious side effects, while others may be lethal. You should avoid dangerous drug mistakes like mixing alcohol and opioids, warfarin and acetaminophen and few others.
-
Atrial Flutter: ECG, Symptoms, and Treatments
Atrial flutter is a problem with the atria of the heart. In atrial flutter the atria of the heart rapidly and repeatedly beat due to an anomaly in the electrical system of the heart. It is a type of arrhythmia and can be dangerous because complications can develop easily. Signs and symptoms of atrial flutter include near fainting, palpitations, mild shortness of breath, and fatigue. While the exact cause of atrial flutter is not clearly understood, it's most likely related to your health, what medical conditions you certainly have, poor diet, lack of exercise, and drinking too much alcohol. Atrial flutter is diagnosed by physical examination, medical history, and a sawtooth ECG wave pattern.
-
Phlebitis (Thrombophlebitis)
Phlebitis is the inflammation of a vein. Thrombophlebitis is when a blood clot causes the inflammation. Phlebitis can be superficial or deeper in the veins. A blood clot deep in a vein is deep vein thrombosis (DVT). Some of the common causes of phlebitis include prolonged inactivity, varicose veins, trauma to a vein, underlying cancers, clotting disorders, and other causes. Symptoms of phlebitis may be mild (pain, tenderness, redness, or bulging of a vein. Treatment of phlebitis depends on the cause.
-
Concussion
A concussion is a short-lived loss of brain function that is due to head trauma. There are two types of concussion, simple and complex. Symptoms of a concussion include headache, nausea, dizziness, dazed feeling, irritability, and visual symptoms. Physical signs include poor concentration, emotional changes, slurred speech, and personality changes. Concussion is diagnosed with physical examination and testing. Treatment for a concussion in general includes treatment for control of the symptoms and time.
-
Omega-3 Fatty Acids
Omega-3 fatty acids are essential fats that help decrease one's cholesterol and triglyceride levels as well as reduce the risk of coronary artery disease. Omega-3s are found in salmon, sardines, walnuts, and canola oil. These fats may help reduce the risk of ventricular fibrillation and sudden cardiac death.
-
Aortic Valve Stenosis
Aortic valve stenosis is an abnormal narrowing of the aortic valve of the heart. The causes of aortic stenosis are wear and tear of the valve in the elderly, congenital, or scarring or scarring of the aortic valve from rheumatic fever. Symptoms include angina, fainting, and shortness of breath. Treatment is dependant upon the severity of the condition.
-
Moyamoya Disease
Moyamoya disease is an inherited (genetic) progressive cerebrovascular disorder caused by arteries that are blocked at the base of the brain. Moyamoya means "puff of smoke" in Japanese. Signs and symptoms of Moyamoya disease in adults include fainting, and vision problems, and in children included may include headaches and speech problems. There are 6 stages of Moyamoya disease. Surgery is the preferred treatment for the disease, and there is no cure for Moyamoya disease, and it can be fatal.
-
Stress and Heart Disease
Stress itself may be a risk factor for heart disease, or high levels of stress may make risk factors for heart disease worse. The warning signs of stress can be physical, mental, emotional, or behavioral. Check out the center below for more medical references on stress and heart disease, including multimedia (slideshows, images, and quizzes), related diseases, treatment, diagnosis, medications, and prevention or wellness.
-
Heart Attack Treatment
A heart attack involves damage or death of part of the heart muscle due to a blood clot. The aim of heart attack treatment is to prevent or stop this damage to the heart muscle. Heart attack treatments included medications, procedures, and surgeries to protect the heart muscle against injury.
-
Priapism (Penis Disorder)
Priapism is a penis disorder characterized by a prolonged, unwanted erection of the penis. Medical conditions, trauma, or medications can cause priapism. There are three categories of priapism: ischemic priapisim, non-ischemic priapism, and stuttering priapism. Treatment includes medical intervention, medication, and at times, surgery.
-
Heart Disease in Women
Heart disease in women has somewhat different symptoms, risk factors, and treatment compared to heart disease in men. Many women and health professionals are not aware of the risk factors for heart disease in women and may delay diagnosis and treatment. Lifestyle factors such as diet, exercise, tobacco use, overweight/obesity, stress, alcohol consumption, and depression influence heart disease risk in women. High blood pressure, high cholesterol, and diabetes also increase women's risk of heart disease. Electrocardiogram (EKG or ECG), stress-ECG, endothelial testing, ankle-brachial index (ABI), echocardiogram, nuclear imaging, electron beam CT, and lab tests to assess blood lipids and biomarkers of inflammation are used to diagnose heart disease. Early diagnosis and treatment of heart disease in women saves lives. Heart disease can be prevented and reversed with lifestyle changes.
-
Superior Vena Cava Syndrome
Superior vena cava syndrome is compression of the superior vena cava vein located in the upper chest. Causes of superior vena cava include lung cancer, lymphoma, other cancers in the chest, blood clots in the superior vena cava, or infection. Symptoms of the syndrome include shortness of breath. Superior vena cava syndrome is diagnosed by ultrasound, chest X-ray, CT scan, and in some cases biopsy. Treatment depends upon the cause of the syndrome.
-
Antiphospholipid Syndrome
Antiphospholipid syndrome (phospholipid antibody syndrome or Hughes syndrome) is an immune system disorder with symptoms that include: excessive blood clotting, miscarriages unexplained fetal death, or premature birth. In antiphospholipid syndrome, these symptoms are accompanied by the presence of antiphospholipid antibodies (cardiolipin or lupus anticoagulant antibodies) in the blood. Treatment focuses on preventing clotting by thinning the blood with the use of anticoagulants and aspirin.
-
Heart Attack Prevention
Heart disease and heart attacks can be prevented by leading a healthy lifestyle with diet, exercise, and stress management. Symptoms of heart attack in men and women include chest discomfort and pain in the shoulder, neck, jaw, stomach, or back.
-
Smoking and Heart Disease
Smoking increases the risk of heart disease in women and men. Nicotine in cigarettes decrease oxygen to the heart, increases blood pressure, blood clots, and damages coronary arteries. Learn how to quit smoking today, to prolong your life.
-
Heart Disease Treatment in Women
Heart disease treatment in women should take into account female-specific guidelines that were developed by the American Heart Association. Risk factors and symptoms of heart disease in women differ from those in men. Treatment may include lifestyle modification (diet, exercise, weight management, smoking cessation, stress reduction), medications, percutaneous intervention procedure (PCI), and coronary artery bypass grafting (CABG). Heart disease is reversible with treatment.
-
Vitamins & Exercise: Heart Attack Prevention Series
Vitamins and exercise can lower your risk for heart attack and heart disease. Folic acid, vitamins, and homocysteine levels are interconnected and affect your risk for heart disease or heart attack. For better heart health, avoid the following fried foods, hard margarine, commercial baked goods, most packaged and processed snack foods, high fat dairy, and processed meats such as bacon, sausage, and deli meats.
-
Heart Attack Prevention Overview
Heart attacks are the major causes of unexpected, sudden death among men and women. A heart attack also is a significant cause of heart failure. The process of developing atherosclerosis (hardening of the arteries) begins early in life. Heart attack prevention should begin in childhood because the atherosclerosis process can not be reversed. The risk of having a heart attack increases if you have diseases or conditions such as high blood pressure, diabetes, and other heart conditions.
Treatment & Diagnosis
- Heart Disease FAQs
- Stroke FAQs
- Atrial Fibrillation A-Fib FAQs
- How To Reduce Your Medication Costs
- Pharmacy Visit, How To Get The Most Out of Your Visit
- Indications for Drugs: Approved vs. Non-approved
- Drugs: Buying Prescription Drugs Online Safely
- Drugs: The Most Common Medication Errors
- Medication Disposal
- Dangers of Mixing Medications
- What Pain Medication Can I Take While on Warfarin?
- Can You Have a Joint Aspiration on Coumadin (warfarin)?
- Nosebleeds: First Aid
- Herbs: Toxicities and Drug Interactions
- Head Injury Symptoms, Types, and Severity
- Generic Drugs, Are They as Good as Brand-Names?
Medications & Supplements
Prevention & Wellness
From 
Healthy Heart Resources
Featured Centers
Health Solutions From Our Sponsors

Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
REFERENCE:
FDA Prescribing Information