The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.
Generic drug name:
warfarin
(WAR far in)
Brand name(s):
COUMADIN,
JANTOVEN
GENERIC:
available
FAMILY:
Blood-clotting Inhibitors
Find the drug label by
searching at DailyMed.
Pregnancy and Breast-feeding Warnings [top]
Pregnancy Warning
Warfarin should not be used if you are pregnant or are thinking of becoming pregnant. Severe malformations have occurred in infants of mothers taking this drug. The risk of use of warfarin in pregnant women clearly outweighs any possible benefit.
Breast-feeding Warning
There is no information from either human or animal studies. However, because of the potential for serious adverse effects in nursing infants, you should not take warfarin while nursing.
Safety Warnings For This Drug [top]
Drug Interaction Warning
Increased Risk of Bleeding When Acetaminophen and Warfarin (COUMADIN) Are Taken Together
Acetaminophen may interact with warfarin to increase the risk of bleeding. This risk increases with increasing doses of acetaminophen. The risk of bleeding has been found to increase tenfold in people who were taking 28 or more regular-strength acetaminophen tablets per week, or the equivalent of 18 or more extra-strength tablets per week, compared to those taking warfarin and no acetaminophen.[1] A regular-strength tablet contains 325 milligrams of acetaminophen, and an extra-strength tablet contains 500 milligrams of the drug.
Warfarin is a drug of considerable benefit after heart valve replacement and in preventing blood clots from a type of heart rhythm disturbance known as atrial fibrillation. It also reduces the risk of death, recurrent heart attacks, and stroke after a heart attack.
Based on this new evidence, if you are taking warfarin, you should notify your doctor before taking any product containing acetaminophen.
Black-Box Warning
See full prescribing information for complete boxed warning.
WARNING: BLEEDING RISK
Warfarin sodium can cause major or fatal bleeding.
All patients taking the drug need to undergo routine periodic blood tests to monitor and adjust the warfarin dose.
Drugs, dietary changes, and other factors affect warfarin drug levels.
Instruct patients about prevention measures to minimize risk of bleeding and to report signs and symptoms of bleeding.
Facts About This Drug [top]
Warfarin (COUMADIN, JANTOVEN) reduces the blood’s ability to clot (coagulate) and prevents blood clots from forming in the arteries and veins. It is prescribed to people who have a history of abnormal blood clots or who are at high risk of having abnormal clots.
| Patients over age 60 generally should be taking less than the usual adult dose to lower the risk of heavy bleeding (hemorrhage). After a patient has taken warfarin for three months, a doctor should reevaluate the... |
Warfarin (COUMADIN, JANTOVEN) reduces the blood’s ability to clot (coagulate) and prevents blood clots from forming in the arteries and veins. It is prescribed to people who have a history of abnormal blood clots or who are at high risk of having abnormal clots.
| Patients over age 60 generally should be taking less than the usual adult dose to lower the risk of heavy bleeding (hemorrhage). After a patient has taken warfarin for three months, a doctor should reevaluate the patient's need to continue taking it. |
It is very important that patients take warfarin exactly on schedule because failing to take this drug properly can cause serious adverse effects (see "Adverse effects"). While taking warfarin, a doctor should monitor progress with regular blood tests to ensure that the patient is taking the most effective dose of the drug.
Adverse effects
Bleeding
Bleeding is the most serious adverse effect of warfarin and can be life-threatening. Patients should contact their doctors if they experience any of the following:
Skin necrosis
As of 2005, Australia’s Adverse Drug Reactions Advisory Committee (ADRAC) had received nine reports of death of skin tissue (skin necrosis) with warfarin use, of which three were fatal. The onset occurred within seven days of commencing warfarin in four cases, but in three cases, the first symptoms occurred three to eight weeks after starting warfarin.[2]
In July 2016, the Medicines and Healthcare products Regulatory Agency (MHRA), an agency in the U.K. similar to the Food and Drug Administration (FDA), reported that a rare but serious type of skin necrosis, caused when blood vessels become blocked by an accumulation of calcium (calciphylaxis), was reported in patients taking warfarin.[3]
In September 2016, the FDA added a similar warning of skin necrosis to the drug label for warfarin.[4]
Patients who take warfarin should contact their doctors immediately if they develop a painful skin rash.
Interactions
Warfarin can interact with nearly all drugs. Its anti-clotting action is very difficult to control when other drugs are added or subtracted, or when another drug’s dose is changed. Another medication may either increase or decrease warfarin’s action. While taking warfarin, do not take any other drugs, including nonprescription drugs (such as aspirin, cold remedies, antacids or laxatives) or change the dose of any drug that you currently take without first consulting a doctor.
The MHRA has received seven reports suggesting an interaction between warfarin and the dietary supplement glucosamine, according to the MHRA and the U.K. Committee on Safety of Medicines. In those cases, patients who previously had a stable international normalized ratio (INR, which is a measurement of how properly one’s blood clots) while receiving warfarin experienced an INR increase (abnormal thinning of the blood that can be dangerous) after they started receiving glucosamine supplements.[5] ADRAC reported in February 2008 that it had received 10 reports of an increase in INR values associated with warfarin and glucosamine use.[6]
Results published from a prospective randomized, parallel, double-blind, placebo-controlled study of 45 patients found that acetaminophen (at a dose of 2 or 3 grams a day, administered for 10 days) increased the anticoagulant effect of warfarin in stable patients.[7]
(See “Drug Interaction Warning: Increased Risk of Bleeding When Acetaminophen and Warfarin [COUMADIN] Are Taken Together” in the “Safety Warnings for This Drug” section of this page.)
In 2015, BMJ published a study showing that patients 65 years or older using glipizide or glimepiride concomitantly with warfarin had an increased risk of low blood sugar (hypoglycemia). This risk was highest among patients newly started on warfarin.[8]
In 2018, the Journal of the American College of Cardiology published a study showing an increased risk of bleeding and stroke when warfarin is used with nonsteroidal anti-inflammatory drugs, a class of drugs used to treat pain.[9]
Regulatory actions surrounding warfarin
2006: The FDA announced on Oct. 10 that it would require an agency-approved Medication Guide, which provides information about drug safety, to accompany all new and refill prescriptions for the blood thinner warfarin.[10]
2010: In January, the FDA issued information on the dosage and administration of warfarin. The advisory emphasized that the dose of warfarin must be individualized and that lab monitoring is necessary. The appropriate dose of warfarin is influenced by various factors, stated in the advisory, and not all of the factors leading to the variability in warfarin dose are known.[11]
Before You Use This Drug [top]
Do not use if you have or have had:
Tell your doctor if you have or have had:
When You Use This Drug [top]
How to Use This Drug [top]
Interactions with Other Drugs [top]
Warfarin can interact with a large proportion of drugs and some dietary supplements. Its anticlotting action is very difficult to control when other drugs are added or subtracted, or when another drug’s dose is changed. Another medication may either increase or decrease warfarin’s action. While taking warfarin, do not take any other drugs, including nonprescription drugs (such as aspirin, cold remedies, antacids, laxatives) or dietary supplements, or change the dose of any drug that you currently take, without consulting your doctor first.
The following drugs may cause clinically significant interactions when used together with warfarin[12]. Make sure to tell your doctor and pharmacist about all of the drugs and dietary supplements you are taking and tell them if you are taking any of these interacting drugs:
acetylsalicylic acid, acetaminophen (alone and in combination), ACHROMYCIN, alcohol (if concomitant liver disease), ALURATE, amiodarone, amobarbital, amoxicillin, amoxicillin and clavulanate, amoxicillin/tranexamic rinse, AMOXIL, ANTABUSE, ANTURANE, aprobarbital, ARAVA, aspirin (alone and in combination), ATROMID-S, AUGMENTIN, azathioprine, azithromycin, AZULFIDINE, BACTRIM, BIAXIN, bosentan, butabarbital, BUTAZOLIDIN, BUTISOL, carbamazepine, CARBATROL, CARDIZEM, CARDIZEM CD, CELEBREX, celecoxib, CELEXA, CHIBROXIN, chloral hydrate, chloramphenicol, chlordiazepoxide, CHLOROMYCETIN, cholestyramine, CIPRO, ciprofloxacin, citalopram, clarithromycin, CLINORIL, clofibrate, COMTAN, CORDARONE, COTRIM, cotrimoxazole, DARVON, DARVON-N, dextropropoxyphene, dicloxacillin, DIFLUCAN, DILACOR XR, DILANTIN, diltiazem, disopyramide, disulfiram, DIULO, DURAQUIN, DYCILL, DYNAPEN, EASPRIN, ECOTRIN, EES, EMPIRIN, entacapone, ERYTHROCIN, erythromycin, felbamate, FELBATOL, FELDENE, fenofibrate, FLAGYL, FLOXIN, fluconazole, fluvastatin, fluvoxamine, FORTOVASE, gatifloxacin, gemfibrozil, GENUINE BAYER ASPIRIN, griseofulvin, IMURAN, INDERAL, INDERAL LA, INDOCIN, indomethacin, INH, interferon, INTRON A, INVIRASE, isoniazid, itraconazole, KALETRA, LAMISIL, leflunomide. LESCOL, LESCOL XL, LEVAQUIN, levofloxacin, LIBRIUM, LOCHOLEST, LOPID, LUMINAL, LUVOX, mephobarbital, mesalamine, metharbital, metolazone, metronidazole, MICARDIS, miconazole oral gel, miconazole topical gel, miconazole vaginal suppositories, MONISTAT 1, MONISTAT 3, MONISTAT 7, MONISTAT-DERM, nafcillin, nalidixic acid, NEGGRAM, NOCTEC, norfloxacin, NOROXIN, NORPACE, NORVIR, ofloxacin, PACERONE, PANMYCIN, pentobarbital, Phenobarbital, phenylbutazone, phenytoin, piroxicam, propafenone, propoxyphene, propranolol, QUESTRAN, QUESTRAN LIGHT, QUINAGLUTE DURA-TABS, QUINIDEX, quinidine, REQUIP, ribavirin, RIFADIN, rifampin, RIMACTANE, ritonavir, rofecoxib, ROFERON-A, ropinirole, RYTHMOL, salicylates (topical), saquinavir, SEPTRA, secobarbital, secobarbital and amobarbital, sertraline, simvastatin, SOLFOTON, SPORANOX, sulfasalazine, sulfinpyrazone, sulindac, TEGRETOL, telmisartan, TEQUIN, terbinafine, tetracycline, TIAZAC, TOLECTIN, tolmetin, TRACLEER, tramadol, TRICOR, trimethoprim and sulfamethoxazole, TYLENOL, ULTRAM, VFEND, VIOXX, voriconazole, ZAROXOLYN, ZITHROMAX, ZOCOR, ZOLOFT
Adverse Effects [top]
Call your doctor immediately if you experience:
Call your doctor if these symptoms continue:
Not needing medical attention:
Signs of overdose:
Periodic Tests[top]
Ask your doctor which of these tests should be done periodically while you are taking this drug:
last reviewed June 30, 2024
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