Warfarin

Sounds like 'war-far-in'

Easy-to-read medicine information about warfarin – what it is, how to take warfarin safely and possible side effects.

Type of medicine Also called
  • Blood-thinning medicine
  • Anticoagulant (stops blood clots)
  • Marevan®
  • Coumadin®
Do not change brand without checking with your pharmacist or doctor first.

What is warfarin?

Warfarin is an anticoagulant (it makes it less likely for your blood to clot). It is used to treat clots that have formed in the legs (deep vein thrombosis) or in the lung (pulmonary embolism). Warfarin is also used to stop new clots forming if you are at risk of this happening from atrial fibrillation (irregular heart beat), heart valve replacement, heart attack and major surgery like a hip or knee replacement. Warfarin decreases certain substances (clotting proteins) in your blood.

The following animation describes how warfarin works in the body (British Heart Foundation) 


Dose

  • The dose of warfarin will be different for different people.
  • In New Zealand there are 2 different brands of warfarin tablets — Marevan® and Coumadin®. Do not change brand without checking with your pharmacist or doctor first. Most people take the Marevan® brand. 
  • Warfarin tablets come in different strengths. Each strength is a different colour. You may need to take more than one strength of tablet.
    • Marevan 1mg tablet - brown
    • Marevan 3mg tablet - blue
    • Marevan 5mg tablet - pink
  • Always take your warfarin dose exactly as your doctor or nurse has told you.
  • You will need regular blood tests (INR  tests) to make sure the dose is safe for you.
  • Don't stop taking warfarin until your doctor or nurse tells you to, since stopping too early can put you at greater risk for getting blood clots or stroke.

How to take warfarin

  • Take your tablets (as one dose), once a day, at the same time each day.
  • It is best to take your warfarin in the evening, so you can have your blood test in the morning.
  • You can take warfarin with or without food.
  • Limit alcohol while you are taking warfarin. Alcohol increases your risk of severe bleeding.
  • If you forget to take a dose, take the missed dose if you remember on the same day. If not, skip the dose and carry on as normal. Do not take two doses of warfarin on the same day.
  • Record your missed dose in your anticoagulant booklet and tell your doctor on your next visit.

Precautions while taking warfarin

  • Extra care is needed when taking warfarin because it can cause bleeding.
  • Here are some of the things you need to know: 
    • Blood tests (INR tests)
      You will need to have regular INR blood tests to measure how quickly your blood clots and check your warfarin dose is safe. 
    • Brand name
      Warfarin is available in 2 different brands in New Zealand - Marevan® and Coumadin®. Most people take the Marevan® brand. Always remember the name of the brand you are taking.
    • Diet
      What you eat and drink can affect warfarin. The most important thing is to keep your diet stable. If you make any changes to your diet, tell your doctor.
  • It is important to let health professionals know that you are taking warfarin such as your dentist, your pharmacist, your podiatrist, your nurse. You may need to stop using this medicine for several days before having surgery or medical tests.
  • There is a lot to remember about warfarin. Ask your pharmacist or doctor if there is anything you are unsure of. 
  • Use one of the handouts or patient guides on this page - see Learn more

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Possible side effects

Like all medicines warfarin can cause side effects, although not everyone gets them. Common side effects include nausea (feeling sick) and diarrhoea (runny poos). These may go away with time. Tell your doctor if troublesome.

Increased risk of bleeding

Warfarin increases your risk of bleeding. You might bleed or bruise more easily while you are taking warfarin.

Injuries or falls

Be careful when shaving, clipping fingernails, brushing and flossing your teeth or playing sports. Avoid new tattoos and piercings while taking warfarin; these things may cause bruising and bleeding. Minor bleeding should usually stop on its own. If you have a fall or hurt your head or body, get medical attention immediately, even if you feel okay.

Signs of severe bleeding

If you have any of the following signs of bleeding, contact your doctor immediately or ring Healthline for free 24-hour health advice 0800 611 116

  • becoming pale, very weak and tired, or short of breath
  • any bleeding from the gums, cuts or nosebleeds that won’t stop
  • blood in the stools (poo) – black, tarry stools
  • blood in the urine (wee) – pink, red or brown-coloured urine
  • heavy periods (menstrual bleeding)
  • coughing up blood or vomit that looks like coffee grounds.

Interactions

Warfarin should not be taken with some medications and herbal supplements, so always check with your doctor or pharmacist before starting warfarin or before starting any new medicines. Also check with your pharmacist before taking:

  • over-the-counter anti-inflammatories such as diclofenac (e.g. Voltaren Rapid), ibuprofen (e.g. Nurofen), naproxen (e.g. Naprogesic)
  • herbal extracts such as garlic, ginkgo or ginseng.

Taking these together with warfarin may increase your risk of bleeding and should be avoided.

Learn more

Starting on warfarin Pharmac
Reducing harm from high-risk medicines - Warfarin Health Quality and Safety Commission  
Taking your warfarin medication Bestpractice
Marevan®  Medsafe Consumer Information
Anticoagulants Heart Foundation New Zealand
Warfarin ebook Aspen Pharma
Warfarin New Zealand Formulary Patient Information

Credits: Written by Sandra Ponen, Pharmacist, Health Navigator NZ. Reviewed By: Angela Lambie, Pharmacist, Auckland