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 increases the time it takes 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.

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.

Special instructions

  • 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. 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. 

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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.

Possible side effects

Like all medicines, warfarin can cause side effects, but not everyone gets them.

Side effects What should I do?
  • Nausea (feeling sick), indigestion, tummy pain, headache
  • These may go away with time.
  • Tell your doctor if troublesome.
  • Easy bruising or minor bleeding (such as nosebleed, bleeding from cuts)
  • If this gets worse, tell your doctor immediately or ring HealthLine. 0800 611 116
  • Signs of serious bleeding such as coughing up blood, blood in the stools or black, tarry stools (poo), blood in urine (wee), or brown-coloured urine, bleeding from gums, cuts or nosebleeds, heavy periods and feeling weak, tired, or dizzy.
  • Tell your doctor immediately or ring HealthLine. 0800 611 116

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 a pharmacist before taking over-the-counter anti-inflammatories such as diclofenac (e.g. Voltaren Rapid), ibuprofen (e.g. Nurofen), naproxen (e.g. Naprogesic). Taking these with warfarin may increase your risk of bleeding.

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