Brief Answer:
Yes, it can possibly increase bleeding risk.

Detailed Answer:

Hi,

White Willow has been traditionally used since long for pain relief. It's chemical ingredient is salicin which basically works like aspirin. And as Aspirin relieves pain and fever, but also causes thinning of blood, similarly white willow can also cause thinning of blood besides pain relief.

Warfarin is a also a potent drug used to stop blood clotting , So white willow possible can increase this effect , and hence the risk of bleeding is increased. So extreme caution is needed as some times serious bleeding can occur .personally I would advise not to use this (white willow) if some one is on warfarin.
For pain relief, some one on warfarin, only paracetamol is a safe option.

Hope it's clear now. Let me know if you have anything else to ask about it. I would be glad to answer your query.
Regards.
Dr. Rahman

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