Warfarin
Tablet
Quick Summary
Warfarin reduces clotting factors that depend on vitamin K.
Medical Uses
How it's taken
Take at the same time every day. Regular INR blood tests guide the amount you need.
Your doctor decides the right dose for you and how long to take it.
Your doctor decides the right dose for you. Follow their instructions and the label.
Common Side Effects
Bleeding
Bruising and nosebleeds.
Hair thinning
Sometimes.
Rash
Rarely.
Interactions
Many medicines and herbal remedies
Including antibiotics and painkillers; check before starting anything.
Vitamin K-rich foods
Keep your diet consistent rather than avoiding them.
Alcohol
Affects INR.
Critical Warnings
Bleeding
Black Box Warning: Seek urgent help for black stools, vomiting blood, severe headache or bleeding that won't stop.
Tell all doctors and dentists
Before surgery or procedures.
Don't stop suddenly
Without medical advice.
Pregnancy
Black Box Warning: Can harm an unborn baby.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Warfarin: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine
- Warfarin: medicine used to prevent and treat blood clots(opens in a new tab) · NHS