Warfarin is given to help prevent blood clotting. Your medicine belongs to a group called Anticoagulants (a substance which helps to prevent thrombosis or blood clotting).

Why have I been prescribed Warfarin?

Warfarin is given to help prevent blood clotting. Your medicine belongs to a group called Anticoagulants (a substance which helps to prevent thrombosis or blood clotting).

How does it work?

Warfarin works by preventing the production of chemicals in the body that cause the blood to clot.

When and how do I take it?

Swallow the tablets whole with a drink of water.

  • Try to take the tablets at the same time each day.
  • Do not take more tablets than your doctor tells you to.
  • Do not stop taking your tablets except on your doctor’s or Pharmacists advice.
  • If you miss a dose and remember within two or three hours, you can still take that dose.
  • If you forget your dose for a longer time, do not take that dose to catch up, but take your next dose when it is due. Remember to tell your doctor when you see him/her next and have your blood test.

Avoid dramatically increasing the amount of leafy green vegetables you eat while on warfarin as they can affect the way it works. There is no need to stop eating them or decrease the amount you eat. The key is to stay consistent in everything you eat.

What’s the dose?

The dose varies for everybody and usually requires weekly reviews. Take exactly as is directed by your doctor (he may write it in a yellow book).

Could it interact with other tablets?

Tell your doctor or pharmacist if you are taking any other medications for the treatment of the following conditions:

  • Heart problems e.g. amiodarone
  • Problems with platelet aggregation (blood cells sticking together) e.g. dipyridamole
  • Depression e.g. amitriptyline, nortriptylline
  • Pain and inflammation e.g. azapropazone and diflunisal
  • Pain e.g. paracetamol or any other non-steroidal anti-inflammatory drug.
  • High levels of lipids (fats) in the blood e.g. bezafibrate, gemfibrozil and clofibrate
  • Infection e.g. cefamandole, chloramphenicol, neomycin, co-trimoxazole, fluconazole, ketoconazole, metronidazole, miconazole, nalidixic acid, norfloxacin, sulphonamides, tetracyclines, rifampicin.
  • Stomach ulcers or excessive production of stomach acid e.g. cimetidine, omeprazole, sucralfate.
  • Endometriosis, menstrual problems e.g. danazol
  • Diabetes e.g. tolbutamide and glucagon
  • Gout e.g. allopurinol
  • Cancer e.g. tamoxifen
  • Insomnia e.g. chloral hydrate
  • Hyperactivity e.g. methylphenidate
  • Chronic alcoholism e.g. disulfiram
  • Thyroid problems
  • Epilepsy
  • Oral contraceptives, sedatives or anabolic steroids.
  • Vitamin supplements, e.g. Vitamin K or Cod Liver Oil (or other dietary intake high in fats or oils)

Tell your doctor if you are taking any of the following medicines e.g colestyramine, dextropropoxyphene, feprazone, phenformin, phenylbutazone, fenylramidol, piroxicam, propafenone, quinidine, sulindac, fluorouracil, triclofos, carbamazepine, dichloralphezone, ethchlorvynol, gluthethimide, griseofulvin, primidone, ACTH & phenytoin.

  • The herbal remedy St John’s Wort (Hypericum perforatum) should not be taken at the same time as this medicine
  • You should avoid drinking cranberry juice or taking other cranberry products (for example capsules of concentrates), since it may increase the effects of warfarin in “thinning” the blood.

Herbal supplements should be used with caution and only after informing your doctor first.

What are the possible risks or side-effects?

These tablets sometimes cause unwanted effects in some people. If you get any of the following, tell your doctor:

  • Skin rash or loss of hair
  • Fever
  • Nausea, vomiting or diarrhoea
  • Jaundice (yellowing of the skin or whites of the eyes)
  • Purple discoloration to any other part of your skin e.g. toes
  • Change in the colour of urine since a dark red or brown urine might be due to bleeding in the kidneys or bladder.
  • Bleeding from the nose without any apparent cause. Black or red faeces can indicate internal bleeding.
  • Tell your doctor if you suddenly develop a fever, or unusual symptoms such as pain, swelling, discomfort or you have any difficulty in breathing.
  • Or if these tablets upset you in any other way, tell your doctor or pharmacist.

Because your blood will be thinner, you will notice you bleed for longer if you cut yourself. This is normal just apply pressure to stop the bleeding. What you need to look out for is any unusual bleeding or bleeding you can’t explain.

Can I drink alcohol while taking it?

Like with the diet, the key is consistency. It is ok to drink small amounts while on warfarin dramatic changes in how much you drink will affect how the medicine works.

What if I’m pregnant/breastfeeding?

  • Warfarin should not be given during pregnancy.
  • Warfarin does not pose a major risk while breast feeding.

If you have any more questions please ask your Pharmacist.

Remember to keep all medicines out of reach of children
Please Note
: We have made every effort to ensure that the content of this information sheet is correct at time of publish, but remember that information about drugs may change. This sheet does not list all the uses and side-effects associated with this drug. For full details please see the drug information leaflet which comes with your medicine. Your doctor will assess your medical circumstances and draw your attention to any information or side-effects which may be relevant in your particular case.