Warfarin – Uses, Dosage, Side effects, interaction

Use, Dose, Side effects, Interaction, Precaution, warning, Expert Advice, FAQs and other details of Warfarin

Warfarin Classification and General Details.

  • Category : Anticoagulants
  • Schedule : Schedule “H”
  • Prescription : Required
  • Legal Status : Approved
  • Available as : Tablets , Powder for Injection (discontinued)

Description of Warfarin

Warfarin is an Oral anticoagulant which is used to prevent the blood from clotting.

Oral means it’s taken by mouth. An anticoagulant is a medicine that stops blood clotting.

You should inform the doctor if you have any bleeding disorder before taking this medicine and you should be aware of the possible side effects of this medicine.

Close monitoring of liver and kidney function is necessary while receiving this medicine due to an increase in the risk of bleeding.

Clotting (thickening) is a complex process involving a number of substances called clotting factors.

Clotting factors are produced by the liver and help control bleeding. They work with cells that trigger the clotting process (platelets) to ensure blood clots effectively.

To produce some of the clotting factors, the liver needs a good supply of vitamin K.

Warfarin blocks one of the enzymes (proteins) that uses vitamin K to produce clotting factors. This disrupts the clotting process, making it take longer for the blood to clot.

Uses of Warfarin

Why and When Warfarin is prescribed for?

Warfarin is commonly called a “blood thinner,” but the more correct term is “anticoagulant.” It helps to keep blood flowing smoothly in your body by decreasing the amount of certain substances (clotting proteins) in your blood.

Anticoagulant medicines, such as warfarin, are often prescribed for people who’ve had a condition caused by a blood clot, such as:

Heart Attack : Prescribed in Heart attack

Stroke : Prescribed in Heart stroke

Deep vein thrombosis : a blood clot within a deep vein in the body, usually in a leg, Warfarin is used to prevent the blood clot formation in legs and other extremities.

Pulmonary embolism : Warfarin is used in the treatment of Pulmonary embolism (blood clot in the lung) by improving the blood flow in the lungs.

Prophylaxis for Myocardial Infarction : Warfarin is used to prevent the formation of clots in vessels that supply blood to the heart. This helps in preventing a heart attack.

Prevention of Thromboembolism in Atrial Fibrillation : Warfarin is used to prevent blood clot formation in patients with heart disorders like atrial fibrillation (irregular heartbeat).

Warfarin may also be prescribed for people at an increased risk of developing harmful blood clots, such as those with:

  • a replacement or mechanical (prosthetic) heart valve
  • an irregular heart rhythm, known as atrial fibrillation
  • a blood clotting disorder, such as thrombophilia
  • an increased risk of blood clots following surgery

Side effects / Adverse Effects

What are the Major & minor side effects for Warfarin?

When you take warfarin, your blood won’t clot as easily. If you accidentally cut yourself while taking warfarin, you may bleed heavily. However, the risk of a major bleeding event is low.]

  • Abdominal pain
  • Blurred vision
  • Blood in urine and stools
  • Headache
  • Dizziness
  • Diarrhea
  • Skin rash and itching
  • Yellow colored eyes or skin
  • Muscle or joint pain
  • Excessive air or gas in stomach
  • Hair loss or thinning of the hair

Warfarin side effects that require immediate medical attention

  • Severe bleeding, including heavier than normal menstrual bleeding
  • Red or brown urine
  • Black or bloody stool
  • Severe headache or stomach pain
  • Joint pain, discomfort or swelling, especially after an injury
  • Vomiting of blood or material that looks like coffee grounds
  • Coughing up blood
  • Bruising that develops without an injury you remember
  • Dizziness or weakness
  • Vision changes

You should therefore seek medical attention if you:

  • pass blood in your urine or faeces
  • pass black faeces
  • have severe bruising
  • have long nosebleeds – lasting more than 10 minutes
  • have bleeding gums
  • cough up blood or have blood in your vomit
  • experience unusual headaches
  • have heavy or increased bleeding during your period, or any other bleeding from your vagina (in women)

What precautions can you take against Warfarin and it’s side effects?

To reduce your chance of developing Warfarin side effects:

  • Tell your doctor about any other medications or supplements you take.
  • Before taking warfarin, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies.
  • Avoid situations that increase your risk of injury.
  • Take care when shaving and brushing your teeth
  • Wear protective clothing when gardening, sewing or playing contact sports
  • Use insect repellent to avoid insect bites or stings
  • Tell Doctors if you take Warfarin before you have any medical or dental procedures.
  • Consider wearing a bracelet or carrying a card that says you take warfarin.
  • Consider a Warfarin sensitivity test.

When not to use?

Contraindications of Warfarin 

Allergy : This medicine is not recommended for use in patients with a known allergy to Warfarin.

Central nervous system bleeding : This medicine is not recommended for use in patients with a head and/or spinal cord injury.

Bleeding disorder : This medicine is not recommended for use in patients who have a known history of bleeding disorders or an active bleeding disorder (inability of the blood to clot normally).

Gastrointestinal disorders : This medicine is not recommended for use in patients with a known history of gastrointestinal disorders like peptic ulcer disease or gastrointestinal bleeding due to an increase in the risk of further bleeding.

Warfarin Dosage

Dosing of Warfarin is complicated because it is known to interact with many commonly used medications and certain foods.

When initiating warfarin therapy (“warfarinization”), the doctor will decide how strong the anticoagulant therapy needs to be.

The maintenance dose of Warfarin can fluctuate significantly depending on the amount of vitamin K1 in the diet. Keeping vitamin K1 intake at a stable level can prevent these fluctuations.

Leafy green vegetables tend to contain higher amounts of vitamin K1.

Green parts of members of the family Apiaceae, such as parsley, cilantro, and dill, are extremely rich sources of vitamin K; cruciferous vegetables such as cabbageand broccoli, as well as the darker varieties of lettuces and other leafy greens, are also relatively high in vitamin K1.

Green vegetables such a peas and green beans do not have such high amounts of vitamin K1 as leafy greens. Certain vegetable oils have high amounts of vitamin K1. Foods low in vitamin K1 include roots, bulbs, tubers, and most fruits and fruit juices. Cereals, grains and other milled products are also low in vitamin K1.

Missed Dose

Take the missed dose as soon as you remember. If it is almost the time for your next scheduled dose, then the missed dose should be skipped.

If you usually take Warfarin in the morning and forget to take it at your normal time, take it as soon as you remember and continue as normal.

If you forget to take your dose of warfarin in the evening but remember before midnight on the same day, take the missed dose.

If midnight has passed, leave that dose and take your normal dose the next day at the usual time.

Consult your doctor for proper information


Seek emergency medical treatment or contact the doctor in case of an overdose.

Interaction of Warfarin

Drug/Food interactions may change how your medications work or increase your risk for serious side effects. 

Warfarin may interact differently for person to person. You should check all the possible interactions with your doctor before starting any medicine.

Interaction with Alcohol : MODERATE

Getting drunk is dangerous while taking warfarin. It may increase the effect of the drug, increasing the risk of bleeding.

Consumption of alcohol will increase the concentration of Warfarin by inhibiting its metabolism and decreasing synthesis of clotting factors.

Alcohol consumption is not recommended in patients receiving Warfarin due to an increase in the risk of bleeding. Close monitoring of prothrombin time and symptoms like excessive bleeding is necessary if alcohol is consumed with Warfarin.

Interaction with Medicines :

Warfarin can interact with many other medicines.

  • Ethinyl Estradiol : MODERATE
  • Aspirin : SEVERE
  • Proton pump inhibitors : MODERATE
  • Fluoroquinolone antibiotics : SEVERE

List of Medicines with SEVERE interaction

  • abciximab
  • allopurinol
  • amiodarone
  • amobarbital
  • anagrelide
  • antithrombin alfa
  • antithrombin iii
  • argatroban
  • azithromycin
  • bazedoxifene/conjugated estrogens
  • bemiparin
  • bezafibrate
  • bivalirudin
  • butabarbital
  • butalbital
  • capecitabine
  • carbamazepine
  • cefamandole
  • cefazolin
  • cefdinir
  • cefditoren
  • cefotetan
  • cefoxitin
  • cefpodoxime
  • ceftriaxone
  • cefuroxime
  • ceritinib
  • chloral hydrate
  • chloramphenicol
  • cilostazol
  • cimetidine
  • ciprofibrate
  • ciprofloxacin
  • clarithromycin
  • clotrimazole
  • conjugated estrogens
  • dabigatran
  • dabrafenib
  • dalteparin
  • danazol
  • dipyridamole
  • duloxetine
  • edoxaban
  • efavirenz
  • enoxaparin
  • eptifibatide
  • erythromycin base
  • erythromycin ethylsuccinate
  • erythromycin lactobionate
  • erythromycin stearate
  • escitalopram
  • estradiol
  • estrogens conjugated synthetic
  • estropipate
  • ethinylestradiol
  • fenofibrate
  • fenofibrate micronized
  • fenofibric acid
  • fluconazole
  • fluoxetine
  • fluoxymesterone
  • fluvoxamine
  • fondaparinux
  • gemfibrozil
  • heparin
  • hexobarbital
  • ifosfamide
  • imatinib
  • itraconazole
  • ivosidenib
  • ketoconazole
  • lepirudin
  • levomilnacipran
  • levonorgestrel intrauterine
  • levonorgestrel oral
  • levothyroxine
  • liothyronine
  • mesterolone
  • mestranol
  • metronidazole
  • miconazole vaginal
  • milnacipran
  • nafcillin
  • nefazodone
  • nitazoxanide
  • oxandrolone
  • oxymetholone
  • paroxetine
  • pefloxacin
  • pentobarbital
  • phenindione
  • phenobarbital
  • piperacillin
  • posaconazole
  • prasugrel
  • primidone
  • protamine
  • quinine
  • rifabutin
  • rifampin
  • ritonavir
  • roxithromycin
  • secobarbital
  • segesterone/ethinyl estradiol
  • sertraline
  • st john’s wort
  • sulfadiazine
  • sulfamethoxazole
  • sulfisoxazole
  • tamoxifen
  • tenecteplase
  • tesamorelin
  • testosterone
  • testosterone buccal system
  • testosterone intranasal
  • testosterone topical
  • thyroid desiccated
  • tibolone
  • ticlopidine
  • tinzaparin
  • tirofiban
  • trazodone
  • venlafaxine
  • vitamin k1 (phytonadione)
  • voriconazole

List of Medicine with MODERATE interaction

  • acalabrutinib
  • aceclofenac
  • acemetacin
  • acetaminophen
  • agrimony
  • alfalfa
  • alteplase
  • american ginseng
  • amikacin
  • amiodarone
  • amobarbital
  • amoxicillin
  • ampicillin
  • anamu
  • anticholinergic/sedative combos
  • apalutamide
  • aprepitant
  • armodafinil
  • artemether/lumefantrine
  • aspirin
  • aspirin rectal
  • aspirin/citric acid/sodium bicarbonate
  • atazanavir
  • azapropazone
  • azathioprine
  • azficel-t
  • betrixaban
  • bicalutamide
  • blinatumomab
  • bortezomib
  • bosentan
  • brodalumab
  • budesonide
  • bupropion
  • butabarbital
  • butalbital
  • cannabidiol
  • carbamazepine
  • cefaclor
  • cefdinir
  • cefixime
  • cefotaxime
  • cefpodoxime
  • cefprozil
  • ceftazidime
  • ceftibuten
  • ceftizoxime
  • ceftriaxone
  • cefuroxime
  • celecoxib
  • chitosan
  • cholestyramine
  • choline magnesium trisalicylate
  • cigarette smoking
  • cimetidine
  • cinnamon
  • citalopram
  • clarithromycin
  • clindamycin
  • clobetasone
  • clopidogrel
  • cobicistat
  • colesevelam
  • collagenase clostridium histolyticum
  • conivaptan
  • conjugated estrogens, vaginal
  • cordyceps
  • cornsilk
  • cortisone
  • cyclophosphamide
  • cyclosporine
  • daclatasvir
  • danshen
  • darifenacin
  • darunavir
  • dasatinib
  • deferasirox
  • deflazacort
  • delavirdine
  • devil’s claw
  • dexamethasone
  • dhea, herbal
  • diclofenac
  • dicloxacillin
  • diflunisal
  • disulfiram
  • dong quai
  • dronabinol
  • dronedarone
  • dulaglutide
  • dupilumab
  • econazole topical
  • efavirenz
  • elbasvir/grazoprevir
  • eluxadoline
  • elvitegravir/cobicistat/emtricitabine/tenofovir df
  • epoprostenol
  • erythromycin base
  • erythromycin ethylsuccinate
  • erythromycin lactobionate
  • erythromycin stearate
  • eslicarbazepine acetate
  • estrogens esterified
  • ethanol
  • ethinylestradiol
  • ethotoin
  • etodolac
  • etoricoxib
  • etravirine
  • eucalyptus
  • exenatide injectable solution
  • exenatide injectable suspension
  • felbamate
  • fenbufen
  • fennel
  • fenoprofen
  • feverfew
  • fish oil
  • fish oil triglycerides
  • fleroxacin
  • fluconazole
  • fludrocortisone
  • fluorouracil
  • fluoxetine
  • flurbiprofen
  • flutamide
  • fluvastatin
  • fluvoxamine
  • food
  • forskolin
  • fosamprenavir
  • fosphenytoin
  • garlic
  • gefitinib
  • gemcitabine
  • gemifloxacin
  • ginger
  • ginkgo biloba
  • glecaprevir/pibrentasvir
  • glucagon
  • grapefruit
  • green tea
  • griseofulvin
  • guselkumab
  • hemin
  • hexobarbital
  • horse chestnut seed
  • hydrocortisone
  • ibrutinib
  • ibuprofen
  • ibuprofen iv
  • icosapent
  • indinavir
  • indomethacin
  • iodine (radioactive)
  • isoniazid
  • itraconazole
  • ivermectin
  • ixekizumab
  • kanamycin
  • ketoconazole
  • ketoprofen
  • ketorolac
  • ketorolac intranasal
  • ledipasvir/sofosbuvir
  • leflunomide
  • letermovir
  • levocarnitine
  • levofloxacin
  • lofepramine
  • lomitapide
  • lornoxicam
  • lovastatin
  • lumacaftor/ivacaftor
  • lumefantrine
  • marijuana
  • meclofenamate
  • mefenamic acid
  • melatonin
  • meloxicam
  • mercaptopurine
  • mesalamine
  • methimazole
  • methylphenidate
  • methylprednisolone
  • methyltestosterone
  • metronidazole
  • mexiletine
  • miconazole vaginal
  • mistletoe
  • mitotane
  • modafinil
  • moxifloxacin
  • nabumetone
  • naproxen
  • nateglinide
  • nelfinavir
  • neomycin po
  • netilmicin
  • nettle
  • nevirapine
  • nifedipine
  • nilotinib
  • nilutamide
  • nintedanib
  • nitisinone
  • obeticholic acid
  • ofloxacin
  • omadacycline
  • ombitasvir/paritaprevir/ritonavir
  • ombitasvir/paritaprevir/ritonavir & dasabuvir
  • omega 3 carboxylic acids
  • omega 3 fatty acids
  • omeprazole
  • oritavancin
  • orlistat
  • ospemifene
  • oxaprozin
  • oxcarbazepine
  • oxiconazole
  • panax ginseng
  • parecoxib
  • paromomycin
  • pau d’arco
  • pegaspargase
  • peginterferon alfa 2a
  • peginterferon alfa 2b
  • pentobarbital
  • pentoxifylline
  • phenobarbital
  • phenytoin
  • phytoestrogens
  • pipemidic acid
  • piroxicam
  • porfimer
  • posaconazole
  • prednisolone
  • prednisone
  • primidone
  • propafenone
  • propranolol
  • propylthiouracil
  • quinidine
  • quinupristin/dalfopristin
  • regorafenib
  • reishi
  • reteplase
  • rifabutin
  • rifampin
  • rifapentine
  • rifaximin
  • ritonavir
  • rivaroxaban
  • romidepsin
  • rosuvastatin
  • rufinamide
  • salicylates (non-asa)
  • salsalate
  • sarecycline
  • sarilumab
  • saw palmetto
  • schisandra
  • secobarbital
  • secukinumab
  • segesterone/ethinyl estradiol
  • siberian ginseng
  • siltuximab
  • simvastatin
  • sitaxentan
  • smoking
  • sodium zirconium cyclosilicate
  • sofosbuvir
  • sofosbuvir/velpatasvir
  • spironolactone
  • streptomycin
  • sulfamethoxazole
  • sulfasalazine
  • sulindac
  • tamsulosin
  • teduglutide
  • teriflunomide
  • ticagrelor
  • ticarcillin
  • ticlopidine
  • tigecycline
  • tinidazole
  • tipranavir
  • tobacco use
  • tobramycin
  • tolfenamic acid
  • tolmetin
  • topiramate
  • toremifene
  • triamcinolone acetonide injectable suspension
  • triclofos
  • ustekinumab
  • valproic acid
  • vemurafenib
  • venetoclax
  • verapamil
  • vorapaxar
  • voriconazole
  • vorinostat
  • vortioxetine
  • voxilaprevir
  • zafirlukast
  • zileuton

List of Medicine with MINOR Interaction

  • acetaminophen iv
  • acetaminophen rectal
  • alprostadil intracavernous/urethral
  • amobarbital
  • armodafinil
  • ascorbic acid
  • butabarbital
  • butalbital
  • ceftaroline
  • chlorella
  • coenzyme q10
  • colestipol
  • cranberry
  • demeclocycline
  • dexmethylphenidate
  • dimenhydrinate
  • doxycycline
  • efavirenz
  • esomeprazole
  • etravirine
  • felbamate
  • felodipine
  • fluconazole
  • glyburide
  • hexobarbital
  • horseradish
  • lymecycline
  • metronidazole topical
  • metronidazole vaginal
  • mineral oil
  • minocycline
  • modafinil
  • omeprazole
  • oxcarbazepine
  • oxytetracycline
  • parecoxib
  • parsley
  • pentobarbital
  • phenobarbital
  • primidone
  • raloxifene
  • ribavirin
  • rifampin
  • rolapitant
  • rose hips
  • secobarbital
  • sucralfate
  • tetracycline
  • verteporfin
  • vitamin e
  • voriconazole
  • watercress

Disease interactions

Bleeding disorders : SEVERE

Warfarin is not recommended in patients with a history of bleeding disorders or an active bleeding disorder (inability of the blood to clot normally) due to an increase in the risk of further bleeding. Replacement with a suitable alternative should be done under your doctor’s supervision.

Liver Disease : SEVERE

Warfarin is not recommended in patients with a liver injury/disease due to an increase in the risk of bleeding. Close monitoring of liver function and symptoms like blood in the urine and stools, dizziness, unusual bleeding, etc. is necessary while receiving this medicine.

Food interactions :

Some food and drink can interfere with the effect of warfarin if consumed in large amounts, including foods that are rich in vitamin K.

Foods containing large amounts of vitamin K include:

  • green leafy vegetables, such as broccoli and spinach
  • vegetable oils
  • cereal grains

Small amounts of vitamin K can also be found in meat and dairy foods.

Lab interactions : Information not available.

Warfarin in Pregnancy

Warfarin is contraindicated in pregnancy, as it passes through the placental barrier and may cause bleeding in the fetus; warfarin use during pregnancy is commonly associated with spontaneous abortion, stillbirth, neonatal death, and preterm birth.

Warfarin is not recommended for use in pregnant women except in life-threatening conditions where the potential benefits outweigh the risks. Discuss all the risks and benefits with your doctor before taking this medicine.

Coumarins (such as warfarin) are also teratogens, that is, they cause birth defects; the incidence of birth defects in infants exposed to warfarin in utero appears to be around 5%, although higher figures (up to 30%) have been reported in some studies.Depending on when exposure occurs during pregnancy, two distinct combinations of congenital abnormalities can arise.

Warfarin during Breast-feeding

This medicine is recommended for use in breastfeeding women only if clearly needed.

The risks and benefits should be discussed with the doctor before taking this medicine. If the medicine is used, close monitoring of the infant for any undesired effects is necessary.

General warnings


Warfarin is known to cause severe bleeding. It is not recommended in patients with conditions like gastrointestinal bleeding, head injury, and patients about to undergo a surgery. Any symptoms of blood in the stools, vomiting blood, or blood in the urine should be reported to the doctor on priority. Close monitoring of prothrombin time is necessary while receiving this medicine.

Tissue Necrosis

Warfarin may cause tissue death within a few days of the treatment. Close monitoring of symptoms like pain and change in skin color is necessary while receiving this medicine. It is advised to stop the treatment if these symptoms appear. An alternate treatment option should be considered based on the clinical condition.


Warfarin may cause a rare reaction called Calciphylaxis in which calcium is accumulated in small blood vessels of the fat and skin tissues. Close monitoring of symptoms like pain and change in skin color is necessary while receiving this medicine. It is advised to stop the treatment if these symptoms appear. An alternate treatment option should be considered based on the clinical condition.

How Warfarin works?

Warfarin is an anticoagulant. It works by preventing the formation of harmful blood clots. Although it does not dissolve the existing blood clots, it prevents them from growing larger and causing blockages in the blood vessels.

Other Important Details 

Onset of action : The effect of this medicine can be observed in 36 to 48 hours.

Duration of effect : The effect of this medicine lasts for an average duration of 2 to 5 days.

Is it habit forming? : No habit forming tendency has been reported.

Expert Advice for Warfarin

You have been prescribed Warfarin to help prevent blood clots.

For best results, take it at the same time every day.

Your doctor may get regular blood tests done to make sure Warfarin is working properly.

Warfarin increases your risk of bleeding. Be careful while shaving, cutting fingernails or toenails, using sharp objects, or engaging in contact sports (e.g. football, wrestling).

Notify your doctor if you see blood in your vomit, urine or stool (black, tarry stools or bright red blood).

Avoid making sudden major changes to your diet during treatment with this medicine.

If you are going to have a surgery or dental treatment, you may be asked to stop taking Warfarin temporarily.

Do not consume alcohol while taking Warfarin as this may increase its effect.

Do not discontinue use without consulting your doctor as this may increase your chances of having another heart attack or stroke.

Commonly asked Questions / FAQs

Is warfarin an anti-platelet or a beta-blocker drug?

No. Warfarin is not an anti-platelet or beta blocker. It is an anti-coagulant drug

Is Warfarin safer than Xarelto?

Both warfarin and Xarelto (rivaroxaban) are equally safe in the treatment of blood clotting. More precaution required while using these drugs. Always follow the advice of the doctor regarding its use

How long can I take warfarin for?

Warfarin should only be taken for the duration prescribed by your doctor

Is warfarin safe?

Yes. Warfarin is relatively safe if used as recommended. In case of any side-effects, consult your doctor

What can I take for pain/cold if I am taking warfarin?

Please consult your doctor for medicines to be taken with warfarin in case of pain or cold

Can I take warfarin with aspirin, tramadol, Viagra, Tylenol, ibuprofen, or glucosamine?

Warfarin may react with aspirin, tramadol, Viagra, Tylenol, ibuprofen or glucosamine. Please consult your doctor before use

Does warfarin cause constipation, fatigue, headache, or weight gain?

Warfarin may cause constipation, fatigue, headache, or weight gain. If you experience any such symptoms, please consult your doctor.

Can I take Warfarin with Betahistine?

Warfarin and Betahistine can be taken together. No harmful side effects or any other clinical interactions have been seen when the two drugs are taken together.

Can I take Warfarin with sildenafil?

Warfarin can be taken with Sildenafil , no significant drug interactions have been seen between the two. However, there have been some clinical reports of penile fracture in patients using sildenafil with Warfarin. Inform your doctor before taking the two drugs together.

Also Read

Notice : This information is to supplement, not substitute to the judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any medicine, changing any diet or commencing or discontinuing any course of treatment.

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