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Brand Name(s) : Marevan
Side Effects


Warfarin should be used with caution in: the elderly (over 65), people who had stomach ulcers in the past, those with uncontrolled raised blood pressure (hypertension), those who recently had surgery or given birth, those who recently had a stroke, people who take other medicines which increase the risk of bleeding, people with any acute illness, those who have liver or kidney problems, those who drink large amounts of alcohol or are changing their diet (vitamin K content in different foods can vary and this may increase or decrease warfarin effect).

It should not be used in: people allergic to warfarin or any other ingredient in the medicine, women who are pregnant or trying to get pregnant, those who have had had surgery in the last 3 days or have had a baby in the last 2 days, bacterial infections of the heart valves (bacterial endocarditis), severe liver or kidney problems, severe uncontrollable bleeding, haemorrhagic stroke (stroke resulting from bleeding from blood vessels in the brain).

Also see list of precautions and interactions.


Store below 25°C

Oral suspension: once the bottle is opened, it can only be used for 1 month


Warfarin is used to treat a number of problems.

It is a member of a class of drugs called anticoagulants, sometimes known as blood-thinning drugs.

In general, this drug is used to make the blood less viscous (thin the blood), to make undesirable blood clotting less likely.

Benefits of being on this drug include prolonging patients' life and reducing the likelihood of heart or blood system problems, including heart attack or stroke.

Listed below are the typical uses of warfarin:

  • Preventing blood clotting within blood vessels that can lead to the formation of blockages (an embolism or thrombosis)
  • Preventing a blood clot in patients with rheumaticheart disease, atrial fibrillation (a problem with the heart beat rhythm) and in patients following the insertion of an artificial heart valve
  • Prevention and treatment of blood clots within veins (venous thrombosis) and the blood vessel called the pulmonary artery supplying blood to the lung
  • Treatment of transient cerebral ischaemic attacks (sometimes called mini strokes).

However on occasion your doctor may prescribe this medicine to treat a condition not on this list.


How often do I take it?

  • This medication is available as a tablet, which should be taken orally with a glass of water, usually as a single dose every day. It is also available in a liquid form as an oral suspension, which should be taken by mouth, usually as a single dose every day.
  • Follow your doctor’s instructions carefully and make sure you read the label on your medicine to see how many tablets or how much liquid you need to take.
  • It is important to take the correct dose of your medicine. Your dose will be decided by your doctor based on your response (INR) to the medicine.
  • Use this medication regularly in order to get the most benefit from it.
  • Remember to use it at the same time each day - unless specifically told otherwise by your doctor.
  • It may take some time before you notice any benefits of this drug.
  • Certain medical conditions may require different dosage instructions as directed by your doctor.

What dose?

  • Dosage is based on your age, gender, medical condition, response to therapy and use of certain interacting medicines.

Do I need to avoid anything?

  • Avoid drinking large quantities of alcohol, or cranberry juice. You may need to avoid sports which carry a high risk of injury. Consult your doctor or pharmacist for more details.

When can I stop?

  • It is important to continue taking this medication even if you feel well, unless your doctor tells you to stop.


  • Unusual bruising, bleeding, blood in the urine or black, tarry stools
  • Rashes
  • Hair loss
  • Diarrhoea
  • Painful, purple areas on the toes and sides of the feet that whiten with pressure (purple toes syndrome)
  • Yellowing of skin and whites of the eyes (jaundice)
  • Red, swollen patches of skin developing into necrotic (dead) skin (occurs mainly in elderly, overweight women)
If any of these persist or you consider them severe then inform your doctor.

Tell your doctor immediately if you develop any of the following symptoms: purpura (red or purple spots or discolourations of the skin, caused by bleeding under the skin), fever, feeling sick (nausea), vomiting, severe abdominal pain (caused by an inflammation of the pancreas), haemothorax (accumulation of blood in the pleural cavity which is the space between the lungs and the walls of the chest, which can cause swelling and breathing difficulties), or a nosebleed without an apparent cause.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

A serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, itching/swelling (especially of the face/tongue/throat), dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine (which includes vaccines, herbals and over the counter medicines) that you are taking. It is run by the medicines safety watchdog called the Medicines and Healthcare products Regulatory agency (MHRA). Please report any suspected side effect on the Yellow Card Scheme website.


Before taking warfarin, tell your doctor or pharmacist if you are allergic to it; or to other blood-thinning drugs; or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: had surgery in the last 3 days or given birth in the last 2 days, bacterial infections of the heart valves (bacterial endocarditis), severe uncontrollable bleeding, haemorrhagic stroke (stroke resulting from bleeding from blood vessels in the brain), severe liver or kidney problems, or are pregnant.

Before using this medication, tell your doctor or pharmacist your medical history, especially any of the following: history of drinking alcohol to excess, any recent surgery, uncontrolled raised blood pressure (hypertension), any acute illness, kidney or liver problems, stomach ulcers or other stomach or digestive complaints.

Before having surgery or injections into a muscle, tell your doctor or dentist that you are taking this medication.

Does alcohol intake affect this drug?

  • Yes. Avoid drinking alcohol to excess whilst taking warfarin.

Pregnancy and breastfeeding - please ensure you read the detailed information below


Warfarin is not safe to take during pregnancy. Ask your doctor or pharmacist if you have any doubts or questions about this.

It is sensible to limit use of medication during pregnancy whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Warfarin is suitable to take if you are breastfeeding. Ask your doctor or pharmacist if you have any doubts or questions about this.

It is sensible to limit use of medication during breastfeeding whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Before using this medicine, tell your prescriber of all the medicines you are taking including prescription medicines and medicines you have bought over the counter without a prescription. Tell your prescriber if you are taking vitamins or complementary remedies such as herbal products, as these can also interact with medicines.

If you are taking more than one medicine, these may interact with each other. Your prescriber may decide to use medicines which interact with each other if the benefit outweighs the risks. In these cases, the dose of your medicines may need to be adjusted or you may be monitored more closely.

The following may interact with warfarin:

  • Other medicines used to thin the blood e.g. clopidogrel
  • St John's Wort, a herbal remedy used in depression
  • Cranberry juice
  • Anabolic steroids (e.g oxymetholone)
  • Treatments for pain and inflammation (e.g. aspirin, paracetamol, celecoxib, diclofenac, ketorolac, indometacin, mefanamic acid or tramodol)
  • Anti-arrhythmia drugs (to control heartbeat rhythm problems) (e.g. amiodarone or propafenone)
  • Antibiotics (e.g. neomycin, rifampicin, azithromycin, clarithromycin, erythromycin, ofloxacin, chloramphenicol, ampicillin, trimethoprim or sulphonamides)
  • Antidepressants (e.g. venlafaxine, amitriptyline, nortriptyline, paroxetine and fluvoxamine)
  • Diabetes drugs (e.g. tolbutamide or metformin)
  • Antifungals (e.g. miconazole, fluconazole, itraconazole, griseofulvin or ketoconazole)
  • Antivirals (e.g. nevirapine or ritonavir)
  • Cytotoxic drugs, used in cancer patients (e.g. etoposide, ifosfamide, sorafenib, fluorouracil, azothioprine, mercaptopurine, mitotane or erlotinib)
  • Anti-epileptics (carbamazepine or primidone)
  • Stomach ulcer healing drugs (e.g. cimetidine, esomeprazole, omeprazole or sucralfate)
  • Contraceptives (e.g. oestrogens or progesterones)
  • Medicines used to reduce high levels of fat in the blood e.g. bezafibrate, gemfibrozil or to lower cholesterol levels e.g. fluvastatin
  • Others (e.g. vitamin K supplements, dipyridamole, or acitretin)

This information does not contain all possible interactions. Therefore, tell your prescriber of all the products you are using before taking this medicine.

If you have a question or want to discuss anything about your medicine, speak to your local pharmacist.


Abnormal bleeding is the main symptom of a warfarin overdose (e.g. blood in stools or black, tarry stools, blood in urine, red dots under the surface of the skin, excessive menstrual bleeding, excessive bruising or persistent oozing of blood from minor injuries).

If you think you, or someone you care for, might have accidentally taken more than the recommended dose of simvastatin or intentional overdose is suspected, contact your local hospital, GP or if in England call 111. In Scotland call NHS 24. In Wales, call NHS Direct Wales. In the case of medical emergencies, always dial 999.


If you forget a dose and remember within 2 or 3 hours you can still take that dose. If you forget your dose for longer, do not take the dose and wait until your next dose is due. Do not double the dose to catch up. Tell your doctor when you see them next or when you have your next blood test.

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Source: Selected from data included with permission and copyrighted by Boots UK Limited. This copyrighted material is sourced from a licensed data provider and is not for distribution, except as may be authorised by the applicable terms of use.
CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgement of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse events, nor should it be construed to indicate that use of a particular medicine is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any medicine, changing any diet, or discontinuing any course of treatment.

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