Several natural products contain substances that have coumarin, salicylate, or exhibit antiplatelet
properties. Therefore, a theoretical risk for potentiation of the pharmacological activity of warfarin
exists when these herbs are taken with warfarin. Herbs thought to contain coumarin or coumarin
derivatives include the following:
• Angelica root
• Arnica flower
• Anise
• Asafoetida
• Celery
• Chamomile
• Fenugreek
• Horse chestnut
• Licorice root
• Lovage root
• Parsley
• Passionflower herb
• Quassia
• Red clover
• Rue
Meadowsweet, poplar, and willow bark contain high concentrations of salicylates, whereas
bromelain, clove, onion, and turmeric have been reported to exhibit antiplatelet activity. Borage
seed oil contains γ-linoleic acid, which may increase coagulation time. Bogbean has been noted to
demonstrate hemolytic activity, and capsicum has been reported to cause hypocoagulability. There
have been no documented case reports of interaction of warfarin with any of these herbs. However,
patients taking any products containing these herbs concurrently with medications that have anticoagulant
effects, such as warfarin, should be closely monitored for signs or symptoms of bleeding.
Sweet clover also contains coumarin derivatives and therefore poses an increased risk of
bleeding if given with warfarin. There have been no reports of an interaction between sweet clover
and warfarin or hemorrhagic disease in humans. However, several cases of severe hemorrhage and
death have been reported in cattle.



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