St. John's Wort and Warfarin: interaction, severity and spacing
St. John's Wort and Warfarin interact because st. John's Wort induces CYP3A4 and CYP2C9, accelerating warfarin clearance and reducing its anticoagulant effect. Take them with care. Severe risk.
The interaction in detail
| Pair | St. John's Wort and Warfarin |
|---|---|
| Type | Nutrient–drug interaction |
| Severity | Severe |
| Required spacing | None specified |
| Onset | At the time of dosing |
Mechanism
St. John's Wort induces CYP3A4 and CYP2C9, accelerating warfarin clearance and reducing its anticoagulant effect.
What to do
Do not combine. This interaction can cause clot formation. Inform your prescriber if you have been taking it.
How to fit both into one day
Take with food to reduce GI upset. It is a potent enzyme inducer with a long list of interactions — treat it as a medication, not a herb.
An evening dose is conventional so the INR drawn the next morning reflects a stable interval. Keep vitamin K intake consistent.
Putting St. John's Wort in the morning and Warfarin in the evening satisfies the 0-hour separation without disrupting either one's absorption window.