Herbs & Blood Clotting

Herbs & Blood Clotting


Which herbs can affect blood clotting?


Many common herbs and other dietary supplements can increase bleeding risk by increasing the time it takes blood to clot. Using these products can increase the risk of serious bleeding problems, especially if you are going to be having surgery, or are taking anti-coagulant drugs* including:

  • heparin or warfarin (Coumadin)
  • non-steroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin, or
  • COX-2 inhibitors (Vioxx, Celebrex).

*List of medication is not all-inclusive.

Please tell all of your healthcare providers, including your physician, nurse, pharmacist, dietitian, anesthesiologist, surgeon, dentist, and others about all of the prescription and over-the-counter medications and dietary supplements you take.

Your health care team can look for potential interactions between your other medications and dietary supplements and the new medications they may prescribe for you. They can advise you regarding which combinations need to be avoided to minimize the risk of bleeding and serious complications.

If you are taking medications, supplements, or herbs that affect blood clotting, your healthcare team may teach you to watch for signs and symptoms of increased bleeding. These signs include unusual bruising, small red and purple spots visible on the skin (petechia), a rash of purple spots (purpura), and excessive bleeding from cuts or scrapes. If any of these symptoms occur, your doctor or nurse will order blood tests to determine if you are experiencing abnormally slow or fast blood clotting. Your healthcare team can adjust your medications as needed to address these issues. Examples of blood clotting tests include the international normalized ratio (INR) and prothrombin time (PT).

The American Society of Anesthesiologists (ASA) recommends discontinuing all dietary supplements and herbs at least two weeks prior to any surgery. For more information on this topic, watch the ASA video.

Some common herbs and dietary supplements* that can affect blood clotting include:

Angelica Anise Arnica
Borage seed Celery Chamomile
Clove Danshen Fenugreek
Feverfew Garlic Ginger
Ginkgo biloba Ginseng Horse chestnut
Licorice root Onion Papain
Parsley Red clover Sweet clover
Tumeric Willow bark  


*List of herbs, spices, and dietary supplements is not all-inclusive.

The following additional resources provide more detailed information on this topic:

  1. Herbs, Botanicals & Other Products: FAQs
  2. The American Cancer Society booklet Dietary Supplements: How to Know What Is Safe
  3. The Cleveland Clinic, Heart and Vascular Health webpage, Herbal Supplements: Helpful or Harmful?
  4. The ClotCare website
  5. Samuels, N. Herbal Remedies and Anticoagulant Therapy. Thromb Haemost. 2005; 93(1):3-7.

It is vitally important that you tell your healthcare providers about all of the dietary supplements, herbs, vitamins, minerals, and over-the-counter medications you are using. Don't wait for them to ask you. Keep the lines of communication open to safeguard your health and wellbeing.

The original question and answer were generously donated by Diana Dyer, MS, RD a cancer survivor, registered dietitian, organic garlic farmer, and the author of "A Dietitian's Cancer Story: Information & Inspiration for Recovery & Healing from a 3-time Cancer Survivor.

Question and Answer updated by Daria Pori, on behalf on the ON DPG.