St. John's Wort and Warfarin

Publication Date: 
Thu, 09/27/2012
By: Alere Staff

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 Wort does reduce patient INR values.2

Increasing testing frequency is recommended when making any changes to your diet, medication, etc. Studies have shown that increasing testing frequency with weekly testing of INR improves patient safety and helps keep the drug in its therapeutic effective zone.3,4 Weekly testing was shown to be the most effective testing frequency.3 Medicare and many private/commercial insurance reimburse patients for weekly patient self-testing.5 Go to the Getting Started page or call Alere at 1.800.504.4032 for more information about testing your INR at home.

  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.
  3. Am J Manag Care. 2014;20(3):202-209.
  4. Heneghan C., et al. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. 2006. Lancet, 367, 404-11.
  5. Center for Medicare and Medicaid Services. Decision Memo for Prothrombin Time (INR) Monitor for Home Anticoagulation Management  (CAG-00087R) [Memorandum]. 2008. Baltimore, MD.