St. John's Wort and Warfarin

St. John’s Wort has received international attention for its use in mild depression and is commonly used to relieve the conditions that sometimes go along with depression such as anxiety, tiredness, loss of appetite and trouble sleeping.

St. John’s Wort is a long living herb whose yellow flowers and leaves are often used to make herbal supplements. According to the National Institutes of Health, St. John's Wort interacts with many medications, including medications used for depression, contraceptive (birth control) drugs, and medications used for pain and other treatments.

It has also been shown to decrease warfarin’s effectiveness or lower patient International Normalized Ratio (INR) values.1 A study in The Lancet showed that INR decreases from 2.1 to 4.1 fell to 1.1 and 2.1 respectfully when patients started taking St. John’s Wort. While these reductions were specific to the patients studied, individual patients’ response may vary. Literature is consistent that St. John’s Wortdoes reduce patient INR values.2

As always, discuss your diet, medications and any herbal supplements with your doctor.

  1. Yue Q, Bergquist, C, Gerdén, B. Safety of St John's wort (Hypericum perforatum). The Lancet, Volume 355, Issue 9203, Pages 576 - 577, 12 February 2000.
  2. Hammerness P, Basch E, Ulbricht C, et al. St. John's wort: a systematic review of adverse effects and drug interactions for the consultation psychiatrist. Psychosomatics 2003;44:271-82.