What are the side effects of warfarin?

The main side effect of warfarin is bleeding. While the risk of major bleeding is low, you need to be aware of potential problems. For example, you might have trouble stopping the bleeding from a cut on your hand or a nosebleed. More-serious bleeding may occur inside the body (internal).

Seek immediate medical help if you have any of the following:

• Severe bleeding, including heavier than normal menstrual bleeding
• Red or brown urine
• Black or bloody stool
• Severe headache or stomach pain
• Joint pain, discomfort or swelling, especially after an injury
• Vomiting of blood or material that looks like coffee grounds
• Coughing up blood
• Bruising that develops without an injury you remember
• Dizziness or weakness
• Vision changes
• Head injury, even if you're not bleeding

Rarely, warfarin can cause the death of skin tissue (necrosis). This complication occurs within a few days of starting warfarin treatment. Seek immediate medical care if you notice any sores, changes in skin color or temperature, or severe pain on your skin.

Talk to your doctor about these less serious side effects:

• Bleeding from the gums after you brush your teeth
• Bleeding between menstrual periods
• Diarrhea, vomiting or inability to eat for more than 24 hours
• Fever