Heparin and Warfarin

Publication Date: 
Mon, 02/01/2016
By: Alere Staff

Heparin and warfarin are both anticoagulants, medications that decrease new development of blood clots, however they work differently. Heparin is naturally occurring, preventing the formation of clots and the extension of clotting. Meanwhile, warfarin is a vitamin K antagonist that reduces the action of vitamin K to manage clotting. Heparin is used to provide an immediate response while warfarin is generally used for long term treatment. Heparin starts working in your body within 20 to 60 minutes after administration and lasts for 8 to 12 hours. Warfarin is effective 12 to 24 hours after you take it, and peaks at about 1.5 to 4 days, remaining active in your body for 3 to 5 days. For this reason, you will usually be started on heparin and transferred to warfarin within a day or two. You may be kept on both medications until your warfarin dose is therapeutic (INR in range). Heparin is given by injection or IV drip while warfarin is taken orally. Both medications are used to treat:

  • Deep vein thrombosis (DVT): blood clots in the leg veins
  • Pulmonary embolism: blood clots in the lungs
  • Atrial fibrillation: irregular heart beat

The International Normalized Ratio (INR) test is used in managing warfarin dosing. Having a too high an INR means blood clots won’t form quickly enough, which increases your risk of bleeding and bruising. Having too low an INR means the warfarin dose is too low and blood clots could still develop. The Partial Thromboplastin Time, or PTT test, is most often used for patients on Heparin instead of INR.

Both Heparin and Warfarin can interact with other medications, supplements or alcohol so it is always wise to have open communication with your healthcare provider regarding your diet and lifestyle. Multiple clinic trials have shown warfarin can help prevent stroke or heart attack. Stay safe by taking your anticoagulant medication exactly as it is prescribed and making sure you follow your doctor’s orders on lab tests and office visits.


  1. U.S. Department of Health and Human Services. Updated Questions and Answers on Heparin Sodium Injection (Baxter). Food and Drug Administration. August 25, 2010. Retrieved from the website:http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm112606.htm
  2. Healthwise Staff. Unfractionated Heparin for Deep Vein Thrombosis. WebMD. March 12, 2014. Retrieved from the website: http://www.webmd.com/dvt/unfractionated-heparin-for-deep-vein-thrombosis.
  3. Bristol-Myers Squibb Company. Coumadin® (Warfarin Sodium) and You. 2013. Retrieved from the website: http://www.coumadin.com/html/index.htm.
  4. The PROSPER Study. Retrieved from the website: http://prosper-stroke.org/warfarin-study