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Side Effects

Along with its needed effects, a medicine 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 or nurse immediately if any of the following side effects occur:

Less common

  • Abdominal or stomach pain with cramping
  • 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
  • Shortness of breath
  • Sweating
  • Unexplained swelling
  • Unusual tiredness or weakness


  • 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
  • Light-colored stools
  • Loss of appetite
  • Nausea and vomiting
  • Pain in the toes
  • Pain, redness, or sloughing of the skin
  • Pale skin
  • Skin blisters
  • Skin rash
  • Small red or purple spots on the skin
  • Stomach pain
  • Swelling of the eyes or eyelids
  • Tightness in the chest or wheezing
  • Troubled breathing with exertion
  • Unpleasant breath odor
  • Unusual bleeding or bruising
  • Upper right abdominal or stomach pain
  • Vomiting of blood
  • Yellow eyes and skin

Incidence not known

  • Painful or prolonged erection of the penis

Some side effects 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

  • Joint pain
  • Muscle pain


  • 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

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.


It is very important that your doctor check your progress at regular visits to see if the medicine is working properly. Blood tests, such as INR, are needed to check for proper dosage and unwanted side effects. Be sure to keep all appointments.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.

Do not stop taking any of your medicines or start any new medicines unless they have been discussed with your doctor. Keep a list of your medicines with you at all times. This includes prescription medicines, nonprescription (over-the-counter [OTC]) medicines, and herbal or vitamin supplements.

Do not take other medicines that also contain warfarin. Using too much warfarin may cause serious bleeding problems.

Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine several days before having surgery or medical tests.

Check with your doctor immediately if you start to have diarrhea, fever, or any signs of infection.

This medicine may cause skin necrosis or gangrene. Call your doctor right away if you have a pain, color change, or temperature change to any area of your body. Also, call your doctor right away if you have a pain in your toes and they look purple or dark in color. These could be signs of a serious medical problem.

This medicine may increase your chance of bleeding. Check with your doctor right away if you notice any unusual bleeding or bruising; black, tarry stools; blood in the urine or stools; or pinpoint red spots on your skin. Avoid picking your nose. If you need to blow your nose, blow it gently.

Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.

Be careful not to cut yourself when you are using sharp objects, such as a safety razor or fingernail or toenail cutters. Avoid contact sports or other situations where bruising or injury could occur.

It is recommended that you carry identification that says you are using warfarin. If you have any questions about what kind of identification to carry, check with your doctor.

Proper Use

A nurse or other trained health professional will give you this medicine. This medicine is given through a needle placed in one of your veins.

Your doctor will only give you a few doses of this medicine, and then you may be switched to an oral medicine that works the same way. If you have any concerns about this, talk to your doctor.

Carefully follow your doctor’s instructions about any special diet. This medicine works best when you eat about the same amount of vitamin K in your food every day. Avoid big changes in how much vitamin K you eat. Some foods that have a high amount of vitamin K are asparagus, broccoli, brussels sprouts, cabbage, green leafy vegetables (such as collards, turnip greens, mustard greens, spinach, and salad greens), plums, rhubarb, and certain vegetable oils (such as soybean oil and canola oil).

Do not drink alcohol while you are receiving this medicine. Also avoid drinking cranberry juice or eating cranberry products.

Before Using

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of warfarin injection in the pediatric population. Safety and efficacy have not been established.


Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of warfarin injection in the elderly. However, elderly patients may require caution and an adjustment in the dose, especially those who are at risk of bleeding.


Pregnancy Category Explanation
All Trimesters X Studies in animals or pregnant women have demonstrated positive evidence of fetal abnormalities. This drug should not be used in women who are or may become pregnant because the risk clearly outweighs any possible benefit.


Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Drug Interactions

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

  • Tamoxifen

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Abciximab
  • Acenocoumarol
  • Alteplase, Recombinant
  • Amiodarone
  • Anistreplase
  • Aprepitant
  • Aspirin
  • Bivalirudin
  • Capecitabine
  • Carboplatin
  • Celecoxib
  • Chamomile
  • Citalopram
  • Clopidogrel
  • Cyclophosphamide
  • Dabigatran Etexilate
  • Dalteparin
  • Danaparoid
  • Desvenlafaxine
  • Dipyridamole
  • Doxorubicin
  • Dronedarone
  • Drotrecogin Alfa
  • Enoxaparin
  • Eptifibatide
  • Escitalopram
  • Etoposide
  • Etravirine
  • Fenofibrate
  • Fenofibric Acid
  • Fish Oil
  • Fluconazole
  • Fluorouracil
  • Fluoxetine
  • Fluvoxamine
  • Garlic
  • Ginkgo
  • Imatinib
  • Infliximab
  • Influenza Virus Vaccine
  • Ketoprofen
  • Leflunomide
  • Lepirudin
  • Levofloxacin
  • Lycium
  • Marijuana
  • Mechlorethamine
  • Methotrexate
  • Methyl Salicylate
  • Metronidazole
  • Milnacipran
  • Moxifloxacin
  • Naproxen
  • Noscapine
  • Oxandrolone
  • Papaya
  • Paroxetine
  • Phenindione
  • Phenprocoumon
  • Prasugrel
  • Procarbazine
  • Proguanil
  • Reteplase, Recombinant
  • Rivaroxaban
  • Ropinirole
  • Sertraline
  • Simvastatin
  • Sitaxsentan
  • St John’s Wort
  • Streptokinase
  • Sulfamethoxazole
  • Sulfisoxazole
  • Tan-Shen
  • Tenecteplase
  • Testosterone
  • Ticlopidine
  • Tinzaparin
  • Tirofiban
  • Torsemide
  • Urokinase
  • Valproic Acid
  • Venlafaxine
  • Vilazodone
  • Vincristine
  • Vindesine

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Acarbose
  • Acemetacin
  • Acetaminophen
  • Allopurinol
  • Aminoglutethimide
  • Amitriptyline
  • Amoxicillin
  • Amprenavir
  • Apazone
  • Argatroban
  • Atovaquone
  • Avocado
  • Azathioprine
  • Azithromycin
  • Bee Pollen
  • Benzbromarone
  • Black Tea
  • Bosentan
  • Bromfenac
  • Butabarbital
  • Butalbital
  • Carbamazepine
  • Cefamandole
  • Cefazolin
  • Chitosan
  • Chloral Hydrate
  • Cholestyramine
  • Chondroitin
  • Cimetidine
  • Ciprofloxacin
  • Cisapride
  • Clarithromycin
  • Coenzyme Q10
  • Colesevelam
  • Curcumin
  • Cyclosporine
  • Danazol
  • Darunavir
  • Desogestrel
  • Dexamethasone
  • Dexlansoprazole
  • Dicloxacillin
  • Dienogest
  • Diflunisal
  • Disopyramide
  • Disulfiram
  • Dong Quai
  • Doxepin
  • Drospirenone
  • Duloxetine
  • Enoxacin
  • Erlotinib
  • Erythromycin
  • Esomeprazole
  • Estradiol Cypionate
  • Estradiol Valerate
  • Eterobarb
  • Ethinyl Estradiol
  • Ethynodiol Diacetate
  • Etonogestrel
  • Exenatide
  • Felbamate
  • Fluoxymesterone
  • Fluvastatin
  • Gefitinib
  • Gemcitabine
  • Gemfibrozil
  • Ginger
  • Ginseng
  • Glucosamine
  • Glyburide
  • Green Tea
  • Griseofulvin
  • Heparin
  • Ifosfamide
  • Indomethacin
  • Indoprofen
  • Isoniazid
  • Isoxicam
  • Itraconazole
  • Ivermectin
  • Ketoconazole
  • Lactulose
  • Lansoprazole
  • Levamisole
  • Levonorgestrel
  • Lopinavir
  • Lornoxicam
  • Medroxyprogesterone Acetate
  • Melatonin
  • Meloxicam
  • Menthol
  • Mephobarbital
  • Mercaptopurine
  • Mesalamine
  • Mesna
  • Mestranol
  • Methyltestosterone
  • Miconazole
  • Mitotane
  • Moricizine
  • Nafcillin
  • Nalidixic Acid
  • Nelfinavir
  • Nevirapine
  • Nilutamide
  • Nimesulide
  • Norelgestromin
  • Norethindrone
  • Norfloxacin
  • Norgestimate
  • Norgestrel
  • Ofloxacin
  • Omeprazole
  • Oxyphenbutazone
  • Pantoprazole
  • Phenobarbital
  • Phenylbutazone
  • Phytonadione
  • Piracetam
  • Prednisone
  • Primidone
  • Propafenone
  • Propoxyphene
  • Quetiapine
  • Ranitidine
  • Rifabutin
  • Rifampin
  • Ritonavir
  • Rofecoxib
  • Rosuvastatin
  • Roxithromycin
  • Saquinavir
  • Secobarbital
  • Sorafenib
  • Soybean
  • Soy Isoflavones
  • Soy Protein
  • Stanozolol
  • Sucralfate
  • Sulfinpyrazone
  • Sulindac
  • Telithromycin
  • Tenidap
  • Terbinafine
  • Tibolone
  • Ticlopidine
  • Tigecycline
  • Tolterodine
  • Tramadol
  • Trastuzumab
  • Valdecoxib
  • Vancomycin
  • Vemurafenib
  • Vitamin A
  • Vitamin E
  • Vorinostat
  • Zafirlukast
  • Zileuton

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Cranberry Juice
  • Pomegranate

Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • High Protein Food
  • Noni Juice
  • Vitamin K Containing Food

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Alcohol abuse, history of or
  • Mental disorders (e.g., psychosis or senility)—Patients with these conditions or those who cannot cooperate should not be given warfarin.
  • Blood disease or bleeding problems or
  • Heart infection or
  • Hypertension (high blood pressure) or
  • Spinal anesthesia, recent or
  • Stomach or intestinal ulcer, active or
  • Stroke or
  • Surgery, recent or scheduled (e.g., surgery of the eye, brain, or spine) or
  • Threatened miscarriage—Should not be used in patients with any of these conditions. The risk of bleeding from warfarin may be increased.
  • Catheter insertion or
  • Congestive heart failure or
  • Deep venous thrombosis, heparin-induced or
  • Diabetes or
  • Falls or blows to the body or head or
  • Infection or
  • Kidney disease or
  • Liver disease or
  • Major surgery, any type or
  • Protein C deficiency (rare hereditary disease), known or suspected or
  • Thrombocytopenia, heparin-induced or
  • Trauma—Use with caution. This medicine may increase your risk of having serious problems.


Warfarin injection is an anticoagulant. It is used to decrease the clotting ability of the blood and to help prevent harmful clots from forming in the blood vessels. It is often used to prevent or treat deep venous thrombosis, a condition in which harmful blood clots form in the blood vessels of the legs. These blood clots can travel to the lungs and cause a condition called pulmonary embolism. Warfarin is also used to prevent or treat blood clots that are caused by certain heart conditions or open-heart surgery. It may be used after a heart attack to prevent blood clots from forming. Although it will not dissolve blood clots that have already formed, warfarin may keep the clots from becoming larger and causing more serious problems.

This medicine is available only with your doctor’s prescription.