Many medications can cause side-effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Coumadin (Warfarin). If you are concerned about side effects, discuss the risks and benefits of Coumadin (Warfarin) with your doctor.

The following side effects have been reported by at least 1% of people taking Coumadin (Warfarin). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• changes in skin colour
• Diarrhea
• dizziness
• fatigue
• general feeling of being unwell
• headache
• nausea
• weakness

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• heavier-than-normal menstrual bleeding
• numbness or tingling of hands, feet, or face
• rash or itching
• signs of Anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of "purple toe syndrome" (e.g., changing, mottled colour of toes, pain and tenderness of toes, sores that don't heal)
• signs of liver damage (i.e., yellowing of skin or eyes, dark urine, light-coloured stools)
• signs of serious skin damage (e.g., sores, changed skin colour or temperature)
• sudden shortness of breath
• unusual pain or swelling

Stop taking the medication and seek immediate medical attention if any of the following occur:

• fainting
• signs of a serious allergic reaction (i.e., swelling of face or throat, Hives, or difficulty breathing)
• signs of bleeding (dark, tarry stools, bleeding in eye, blood in stools, blood in vomit or vomit that looks like coffee grounds, blood in urine, coughing up blood)
• signs of bleeding in the brain (e.g., sudden or severe headache; sudden loss of coordination; vision changes; sudden slurring of speech; or unexplained weakness, or numbness)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Coumadin (Warfarin).

1 mg
Each pink, scored tablet with "COUMADIN" over "1" on one side contains 1 mg of Coumadin (Warfarin). Nonmedicinal ingredients: D&C Red No. 6 Barium Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

2 mg
Each lavender, scored tablet with "COUMADIN" over "2" on one side contains 2 mg of Coumadin (Warfarin). Nonmedicinal ingredients: FD&C Blue No. 2 Aluminum Lake, FD&C Red No. 40 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

2.5 mg
Each green, scored tablet with "COUMADIN" over "2.5" on one side contains 2.5 mg of Coumadin (Warfarin). Nonmedicinal ingredients: D&C Yellow No. 10 Aluminum Lake, FD&C Blue No. 1 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

3 mg
Each tan, scored tablet with "COUMADIN" over "3" on one side contains 3 mg of Coumadin (Warfarin). Nonmedicinal ingredients: FD&C Blue No. 2 Aluminum Lake, FD&C Red No. 40 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

4 mg
Each blue, scored tablet with "COUMADIN" over "4" on one side contains 4 mg of Coumadin (Warfarin). Nonmedicinal ingredients: FD&C Blue No. 1 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

5 mg
Each peach-coloured, scored tablet with "COUMADIN" over "5" on one side contains 5 mg of Coumadin (Warfarin). Nonmedicinal ingredients: FD&C Yellow No. 6 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

6 mg
Each teal, scored tablet with "COUMADIN" over "6" on one side contains 6 mg of Coumadin (Warfarin). Nonmedicinal ingredients: FD&C Blue No. 1 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake, lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch.

10 mg
Each white, scored tablet with "COUMADIN" over "10" on one side contains 10 mg of Coumadin (Warfarin). Nonmedicinal ingredients: lactose anhydrous, magnesium stearate, and pregelatinized tapioca starch. There is no dye in this product.

Do not take Coumadin (Warfarin) if you:

• are allergic to Coumadin (Warfarin) or any ingredients of the medication
• are pregnant
• are undergoing certain types of surgery
• do not have access to an adequate lab facility to get regular blood tests done
• have a high risk of abortion, eclampsia, and preeclampsia (complications of pregnancy often associated with sudden onset of very high blood pressure)
• have bleeding tendencies associated with active ulcers or overt bleeding of the stomach, genitourinary, or respiratory tracts; heart infection; brain Aneurysm; or bleeding associated with many other medical conditions
• have certain blood disorders
• have malignant hypertension
• have recently had or are planning to have surgery of the central nervous system or the eye or surgery associated with trauma resulting in large open surfaces
• have senility, Alcoholism, or psychosis, or other conditions where you may not be able to cooperate with taking the medication and having the necessary lab tests on a regular basis

Anticoagulation (blood thinning) should not take place in any situation where the risk of bleeding might be greater than the potential benefits of anticoagulation.

There may be an interaction between Coumadin (Warfarin) and any of the following:

• Acetaminophen
• acetylsalicylic acid (ASA)
• Adalimumab
• alcohol
• Allopurinol
• alteplase
• aminosalicylic acid
• Amiodarone
• Anagrelide
• androgens (e.g., Danazol, oxandrolone, testosterone)
• anticancer medications (e.g., Carboplatin, Cyclophosphamide, Fluorouracil)
• Apixaban
• Aprepitant
• atovaquone
• Azathioprine
• "azole" antifungals (e.g., fluconazole, ketoconazole, Voriconazole)
• barbiturates (e.g., pentobarbital, Phenobarbital)
• Bezafibrate
• Bicalutamide
• birth control pills
• Bosentan
• Carbamazepine
• cephalosporins (e.g., cefaclor, cefazolin, cefotetan, cefoxitin, Cephalexin)
• Celecoxib
• chloral hydrate
• Cholestyramine
• Cimetidine
• Clopidogrel
• Cobicistat
• coenzyme Q10
• Colestipol
• corticosteroids (e.g., Dexamethasone, Hydrocortisone, Prednisone)
• cranberry
• dabigatran
• Dasatinib
• Deferasirox
• dexmethylphenidate
• Dipyridamole
• disulfiram
• dong quai
• Dronedarone
• Entacapone
• Enzalutamide
• Erlotinib
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• ethacrynic acid
• Exenatide
• Ezetimibe
• Fenofibrate
• garlic
• Gemfibrozil
• ginger
• ginkgo biloba
• ginseng
• Glucagon
• glucosamine
• green tea
• Heparin
• Hepatitis C antivirals (e.g., daclatasvir, dasabuvir, ledipasvir, letermovir, ombitasvir, simeprevir, sofosbuvir)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delavirdine, efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• imatinib
• Ivacaftor
• Leflunomide
• Linezolid
• Lomitapide
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• Mefloquine
• Methimazole
• methyl salicylate
• Methylphenidate
• Metronidazole
• mifepristone
• milk thistle
• Mirtazapine
• multivitamins with vitamin A, E
• nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., Diclofenac, ibuprofen, Naproxen)
• Obinutuzumab
• omega-3 fatty acids
• Orlistat
• penicillins (e.g., ampicillin, penicillin G, piperacillin, ticarcillin)
• Pentoxifylline
• Phenytoin
• phytonadione (Vitamin K)
• Prasugrel
• primidone
• progestins (e.g., Dienogest, Levonorgestrel, medroxyprogesterone, Norethindrone)
• proguanil
• Propafenone
• Propylthiouracil
• proton pump inhibitors (PPIs; e.g., Esomeprazole, Lansoprazole, Omeprazole)
• Quetiapine
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, Norfloxacin, Ofloxacin)
• Ranitidine
• rifabutin
• rifampin
• ribavirin
• Rivaroxaban
• Romidepsin
• Ropinirole
• St. John's wort
• saw palmetto
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., Desvenlafaxine, Duloxetine, Venlafaxine)
• Sorafenib
• "statins" (e.g., Fluvastatin, Lovastatin, Simvastatin)
• streptokinase
• Sucralfate
• Sulfasalazine
• sulfonamide antibiotics (e.g., sulfadiazine, sulfamethoxazole)
• sulfonylurea Diabetes medications (e.g., chlorpropamide, Gliclazide, Glyburide, Tolbutamide)
• Tamoxifen
• tetracyclines (e.g., doxycycline, Minocycline, Tetracycline)
• Thyroid hormones (e.g., Levothyroxine, Liothyronine, thyroid)
• Ticagrelor
• Ticlopidine
• Tolterodine
• Tramadol
• Trazodone
• tricyclic antidepressants (e.g., Amitriptyline, Clomipramine, Desipramine, Trimipramine)
• urokinase
• vitamin A
• vitamin C
• vitamin E
• Zafirlukast

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Coumadin (Warfarin). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription) and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or illegal drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medication conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Coumadin (Warfarin).

Bleeding: The most serious risk associated with Coumadin (Warfarin) is bleeding in any tissue or organ. The risk of bleeding is related to how much is taken and for how long.

It is extremely important to have regular blood tests (as recommended by your doctor) to ensure that the correct level of blood thinning is occurring. These blood tests measure your INR level to determine the dose of Coumadin (Warfarin). Your health care provider will adjust the dose of Coumadin (Warfarin) depending on the INR level to ensure you are not receiving too little medication (which may result in blood clots forming) or too much medication (which may result in bleeding).

Congestive heart failure: People with congestive heart failure may be more sensitive to the effects of Coumadin (Warfarin). If you have any heart problems, discuss with your doctor how Coumadin (Warfarin) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Coumadin (Warfarin), and whether any special monitoring is needed.

Dental or surgical treatment: It may be necessary to stop taking Coumadin (Warfarin) briefly before scheduled dental or surgical procedures. Make sure that everyone involved in your health care is aware that you are taking Coumadin (Warfarin).

Liver function: Liver disease or reduced liver function may cause Coumadin (Warfarin) to build up in the body, causing side effects, including severe bleeding. If you have liver problems, discuss with your doctor how Coumadin (Warfarin) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Coumadin (Warfarin), and whether any special monitoring is needed.

Medical conditions and other medications: If you have other medical conditions and are taking medications, discuss with your doctor how Coumadin (Warfarin) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Coumadin (Warfarin), and whether any special monitoring is needed.

Some conditions and medications affect the way Coumadin (Warfarin) works and may affect the dosing of Coumadin (Warfarin). Your doctor will recommend you get regular lab tests done.

Non-steroidal anti-inflammatory medications (NSAIDs): It is recommended that anyone taking NSAIDs such as acetylsalicylic acid (Asa) or Ibuprofen should be closely monitored to ensure that no change in anticoagulation dosage is required. NSAIDs can cause stomach ulcers or bleeding. If you notice any signs of bleeding, such as frequent nosebleeds, unexplained bruising, or black and tarry stools, notify your doctor as soon as possible.

Purple toes syndrome: Purple toes syndrome is a complication of Coumadin (Warfarin) treatment and consists of a dark, purplish or mottled colour of the toes, usually occurring 3 to 10 weeks (or later) after starting treatment with Coumadin (Warfarin). Major features of this syndrome include:

• increasing and decreasing of the colour over time
• pain and tenderness of the toes
• purple colour of bottom surfaces and sides of the toes that turns white under moderate pressure and fades with elevation of the legs

Inform your doctor at once if you notice these symptoms.

Pregnancy: Coumadin (Warfarin) should not be used during pregnancy. It may pass to the developing fetus and cause birth defects or death as a result of bleeding. If you become pregnant while taking Coumadin (Warfarin), contact your doctor immediately.

Breast-feeding: It is not known if Coumadin (Warfarin) passes into breast milk. If you are a breast-feeding mother and are taking Coumadin (Warfarin), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of Coumadin (Warfarin) have not been established for children less than 18 years of age. However, the use of Coumadin (Warfarin) by children is necessary in certain situations.