Side effects of warfarin

Specialist Dr John Worthington explains the main side effects of warfarin, what the symptoms are and what to do about them. 


The most serious side effect of warfarin is bleeding. To help reduce your risk of bleeding:

  • make sure you follow the instructions for taking warfarin. This will help keep your INR within your target range
  • be careful when choosing your activities. Avoid those with a risk of injuries that could cause bleeding e.g. an injury or fall.

Some types of bleeding are more serious than others. Ask your health professional what signs and symptoms you need to look out for, when you should contact your doctor about them and when you need to go to a hospital emergency department. Some signs of bleeding may not be obvious, so it is important to know what these are.

Signs and symptoms of bleeding

  • bruising
  • bleeding gums
  • red or dark brown urine
  • red or black bowel motions
  • nosebleeds
  • coughing up blood or blood in your spit
  • trouble breathing or swallowing
  • heavier than usual menstrual periods
  • bleeding from cuts, wounds and scrapes that takes longer to stop
  • dark or blood-stained vomit
  • severe headache or dizziness
  • unexplained pain, swelling or discomfort.

You may occasionally notice bleeding — such as bruises on your body or bleeding gums when you brush your teeth — even when your INR is within your target range. If such bleeding concerns you, is heavier than usual or takes an unusually long time to stop, you should speak to your health professional right away.

Talk to your health professional

Talk to your health professional about ways to reduce your risk of injury and chances of bleeding — for example, by avoiding contact sports, wearing gloves when gardening, making adjustments around the home to reduce your risk of falls, using an electric shaver, and brushing your teeth with a soft-bristled toothbrush. Report any injuries to your health professional — including falls, cuts and scratches, bruising and accidents — even when you don’t notice bleeding.

This is not a complete list of side effects. Occasionally people may experience other side effects with warfarin. If you feel unwell while taking warfarin, even if you do not think it is related to your medicine, you should see your doctor or pharmacist.

Who can I ask about side effects?

If you’re concerned that you or someone in your care may have had side effects related to a medicine, seek medical advice. People with questions about their medicines or seeking general information about side effects can also call the NPS Medicines Line on 1300 633 424 (Monday-Friday, 9am-5pm).To report possible side effects call the Adverse Medicine Events (AME) line on 1300 134 237 from anywhere in Australia (Monday–Friday, 9am–5pm AEST).