Warfarin - Side effects of warfarin

It is important to check for bleeding (haemorrhages) when taking warfarin as anticoagulant medication can cause excessive bleeding.

You must seek medical attention and have an urgent blood test if you experience any of the following:

passing blood in your urine or faeces
passing black faeces
severe bruising
long nosebleeds (lasting longer than 10 minutes)
bleeding gums
blood in your vomit or coughing up blood
unusual headaches
(in women) heavy or increased bleeding during your period, or any other bleeding from the vagina

You must seek immediate medical attention if you:

are involved in a major accident
experience a significant blow to the head
are unable to stop any bleeding

Other common side effects

nausea or vomiting (feeling sick)
diarrhoea
jaundice
hair loss
skin rashes
fever (a temperature of 38C (100.4F) or above)
red or purple patches of skin (purpura)
pancreatitis (inflammation of the pancreas) – which leads to a dull pain around the top of the stomach
kidney problems

See your GP if you experience any persistent side effects while taking warfarin.

Warfarin-induced skin necrosis

In rare cases, warfarin can lead to skin necrosis (tissue death). This condition is caused by blood clots blocking the blood vessels, leading to damaged areas of skin.

The first symptom of skin necrosis is red or purple patches of skin (purpura), followed by blood blisters and then painful skin lesions. There is often a red, net-shaped rash around the damaged skin.

Symptoms are more likely to appear on fatty areas, such as the breasts, abdomen, buttocks and thighs. Symptoms usually appear within the first two to five days after starting to take warfarin.

See your GP immediately if you suspect skin necrosis.