Supplement stacks / St Johns Wort + Warfarin
Can You Take St Johns Wort with Warfarin?
St Johns Wort and Warfarin: one interaction flagged, scored 3/10 (high risk). The count and score come from an AI-written analysis checked against our interaction rules, which can only make it stricter. Not medical advice.
Safety at a glance
This score comes from an AI-written analysis of the pair. Our interaction rules check it and can only make it stricter, never milder. Informational only: it can't account for your medications, conditions, or genetics.
What the AI-written analysis says
St. John's Wort is known to interact with warfarin, potentially reducing its effectiveness and increasing the risk of thromboembolic events. Caution is advised when considering the use of St. John's Wort while on warfarin therapy.
Warfarin is a prescription medication. This page describes publicly documented interactions — it can't see your dose, your other prescriptions, or your labs. Discuss any supplement with the prescriber or pharmacist who manages this medication before combining.
Known interactions
St. John's Wort may induce cytochrome P450 enzymes, leading to decreased warfarin levels and increased risk of clotting.
St. John's Wort
From the AI-written analysis.
Generally considered safe for short-term use, but can interact with many medications, including warfarin.
Typical dosage: 300 mg three times daily of standardized extract
- photosensitivity
- gastrointestinal upset
- fatigue
- Avoid use with warfarin; consult healthcare provider before use.
- May cause serotonin syndrome when combined with other serotonergic agents.
Warfarin
From the AI-written analysis.
Warfarin is an anticoagulant that requires careful monitoring of INR levels to prevent bleeding complications.
Typical dosage: As prescribed or as directed on the label
- bleeding
- bruising
- gastrointestinal upset
- Monitor INR more frequently when starting or stopping St. John's Wort.
- Maintain consistent vitamin K intake.
Also commonly mentioned
These come up in questions about this combination. They are not part of the pair above. From the AI-written analysis.
Vitamin K
Essential for blood clotting; can counteract the effects of warfarin.
Typical dosage: 90-120 mcg daily for adults
- rare allergic reactions
- Keep intake consistent while on warfarin to avoid fluctuations in INR.
- Consult healthcare provider for dietary sources.
Omega-3 Fatty Acids
Generally safe; may have mild anticoagulant effects.
Typical dosage: 1000-3000 mg daily
- fishy aftertaste
- gastrointestinal discomfort
- Monitor for increased bleeding risk when combined with warfarin.
- Consult healthcare provider before starting.
Coenzyme Q10
Generally safe; may have a mild effect on blood pressure and anticoagulation.
Typical dosage: 100-200 mg daily
- gastrointestinal upset
- insomnia
- Consult healthcare provider before use with warfarin; may affect INR levels.
- Monitor for changes in blood pressure.
Timing
No timing arrangement makes this combination safe — see the warnings above.
Watch out for
- St. John's wort speeds up the liver enzymes that clear warfarin, so warfarin can work less well and INR can fall. In a study, two weeks of it made warfarin clear faster. Do not start it on warfarin without asking the anticoagulation clinic or prescriber first. If you already use it, do not stop it or change the amount on your own either: stopping can change INR too. Tell the clinic before any change, and expect INR to be checked around it.
- Do not use St. John's Wort while taking warfarin; consult healthcare provider for alternatives.
- Monitor INR levels closely if considering any new supplements.
Frequently asked questions
Can you take St Johns Wort and Warfarin together?
St Johns Wort and Warfarin: one interaction flagged, scored 3/10 (high risk). The count and score come from an AI-written analysis checked against our interaction rules, which can only make it stricter. Not medical advice.
What score does the St Johns Wort and Warfarin combination get?
The St Johns Wort and Warfarin combination is scored 3/10 (high risk). The score comes from an AI-written analysis checked against our interaction rules, which can only make it stricter. Not medical advice. Always confirm with a healthcare professional.
When should you take St Johns Wort and Warfarin?
No timing arrangement makes this combination safe — see the warnings above.
What should you watch out for when combining St Johns Wort and Warfarin?
St. John's wort speeds up the liver enzymes that clear warfarin, so warfarin can work less well and INR can fall. In a study, two weeks of it made warfarin clear faster. Do not start it on warfarin without asking the anticoagulation clinic or prescriber first. If you already use it, do not stop it or change the amount on your own either: stopping can change INR too. Tell the clinic before any change, and expect INR to be checked around it. Do not use St. John's Wort while taking warfarin; consult healthcare provider for alternatives. Monitor INR levels closely if considering any new supplements.
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Not medical advice
AI-written analysis generated August 11, 2026, checked by our interaction rules · How our analysis works