Can You Take St. John's Wort and Warfarin Together?

What the interaction means

Warfarin's FDA prescribing information states in its Botanical (Herbal) Products and Foods section: "Conversely, some botanicals may decrease the effects of warfarin sodium (e.g., co-enzyme Q10, St. John's wort, ginseng)." St. John's wort is also listed in the label's drug-interaction table as an inducer of CYP1A2, one of the enzyme pathways involved in warfarin metabolism. NCCIH's current St. John's Wort safety page independently corroborates this, naming warfarin among the medicines St. John's wort "can weaken the effects of," and explains the general mechanism: St. John's wort can induce "cytochrome P-450 enzymes and intestinal P-glycoprotein," which affects how the body processes many other medications.

Why it may happen

St. John's Wort induces liver cytochrome P-450 enzymes (including CYP1A2) and intestinal P-glycoprotein, which can speed up the clearance of warfarin and reduce its blood-thinning effect.

Practical context

This is a well-documented, FDA-label-referenced interaction. Because warfarin already carries a boxed warning for bleeding risk and requires careful, individualized dose management via INR monitoring, any change in effect -- weaker or stronger -- from starting, stopping, or changing a St. John's Wort supplement is significant and should be discussed with the prescriber managing anticoagulation, not adjusted independently. This is an ongoing metabolic-enzyme effect, not a same-day absorption-timing issue, so no spacing interval applies.

What the sources say

Related interactions

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• St. John's Wort and CalciumInsufficient evidence
• St. John's Wort and IronInsufficient evidence
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• St. John's Wort and TurmericInsufficient evidence
• Warfarin and IronInsufficient evidence
• Warfarin and MagnesiumInsufficient evidence
• Warfarin and ZincInsufficient evidence
• Warfarin and PotassiumInsufficient evidence
• Warfarin and MelatoninInsufficient evidence
• Warfarin and Vitamin KUse caution
• Warfarin and CiprofloxacinUse caution
• Warfarin and CoQ10 (Coenzyme Q10)Use caution
• Warfarin and CalciumInsufficient evidence
• Warfarin and LisinoprilInsufficient evidence
• Warfarin and SertralineUse caution
• Warfarin and OmeprazoleUse caution
• Warfarin and Vitamin B12Insufficient evidence
• Warfarin and DoxycyclineInsufficient evidence
• Warfarin and CopperInsufficient evidence
• Warfarin and LevothyroxineInsufficient evidence
• Warfarin and MetforminInsufficient evidence
• Warfarin and Vitamin DInsufficient evidence
• Warfarin and SpironolactoneInsufficient evidence
• Warfarin and CaffeineUse caution
• Warfarin and AtorvastatinUse caution
• Warfarin and ProbioticsInsufficient evidence
• Warfarin and CreatineInsufficient evidence
• Warfarin and TurmericInsufficient evidence