Treatments and tests

Warfarin and other medicines

You need to talk to your doctor before making any changes in your medicines.

How do other medicines affect warfarin?

Warfarin is affected by many other medicines. They can change your (INR) and affect the dose of warfarin you need.

When there are changes to your medicine, you may need to have extra blood tests. Changes to your medicines can include:

  • starting a new medicine
  • stopping a medicine
  • changing the dose of a medicine.

All types of medicines can affect (interact with) warfarin including:

  • prescription medicines
  • over-the-counter (OTC) pharmacy medicines
  • vitamins, minerals, herbal medications and dietary supplements.
What should I do with my other medicines?

To minimise the risk of complications with warfarin, let your doctor or pharmacist know:

  • if your regular medicines change
  • before:
    • starting any new medicines
    • taking vitamins, minerals, herbal or natural therapies, including Chinese medicines and OTC medicines.

If you visit a different doctor make sure you tell them you are taking warfarin.

What are some common medicines that interact with warfarin?
Table: Common medicines that interact with warfarin
Medicine type Examples
  • antibiotics
  • anti-inflammatories
  • heart medicines
  • ulcer and reflux medicines
  • pain relievers
  • aspirin
  • ibuprofen
  • naproxen
  • diclofenac
  • cough and cold medicines
  • vitamin C
  • vitamin E
  • vitamin K
Herbal or natural remedies
  • garlic supplements
  • ginger supplements
  • ginseng
  • Ginkgo biloba
  • green tea
  • glucosamine
  • St John’s Wort

There are many more medicines that affect warfarin which are not listed. It is important that your doctor and pharmacist know what medication you are taking.

Can I take aspirin?

Aspirin also affects blood clotting and some doses (Cartia®, Cardiprin® and Astrix®) are used to prevent heart attacks and strokes. If you are taking aspirin check with your doctor whether you need to keep taking it.

Using aspirin to treat pains and fevers should be avoided while taking warfarin. For pain or fever, paracetamol (for example Panadol and Panamax) is safer to use than aspirin as long as it is used at the recommended dose.

Check with your doctor if you need treatment for long-term pain relief.

Where to get help

  • See your doctor.
  • Ring healthdirect Australia on 1800 022 222.

Medic Alert

Medicines information line

Poisons information line

  • Immediate specialist advice for overdoses or poisoning
  • Phone 13 11 26 (local call rates from land line only)

Adverse Medicines Events Line

National Prescribing Service (NPS) MedicineWise


  • Warfarin is affected by many other medicines, including over-the-counter medicines, herbal medicines, supplements and vitamins
  • You should not take aspirin while taking warfarin – use other types of pain relief.


Western Australian Therapeutic Advisory Group | The WA Medication Safety Group

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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