HERBAL MEDICINES OR DIETARY SUPPLEMENTS AND WARFARIN AND OTHER ORAL ANTICOAGULANTS - ST JOHN'S WORT (HYPERICUM PERFORATUM)

St John's wort can cause a moderate reduction in the anticoagulant effects of warfarin.
The CSM in the UK advise that if St John's wort is being taken by patients also taking anticoagulants the herb should be stopped and the anticoagulant dosage adjusted as necessary.