Pharmacology · single question
Which herbal supplements can INCREASE a patient's INR (blood thinning effect) when taken with warfarin?
Show answer and explanation
Correct answer: D. Ginseng, garlic, and St. John's Wort
- A. Iron supplements do not affect INR.
- B. Kale contains vitamin K, which DECREASES INR by supporting clotting factor production — the opposite effect.
- C. Calcium supplements do not significantly affect INR.
- D. Correct. Ginseng, garlic, and St. John's Wort all have blood-thinning or anticoagulant-potentiating effects that can INCREASE INR. St. John's Wort can increase serotonin but also affects anticoagulant metabolism. Patients on warfarin should report all herbal supplement use.