warfarin and St John's Wort

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The interaction of warfarin and St John's wort (SJW) leads to a reduction in the anticoagulant effect of warfarin.

Suggested management of patients taking SJW and warfarin:

  • stop SJW and check INR

  • the INR should be monitored closely because this may rise on stopping SJW

  • it may be necessary to adjust the warfarin dose


  • CEM/CMO/2000/4

Last reviewed 01/2018