Bleeding Disorders and Supplements That Affect Clotting

Call 911 for bleeding that will not stop or after a serious injury. Do not wait to work out whether a supplement is the cause.

For people with a bleeding disorder, such as von Willebrand disease, or who take a blood thinner, the question "does this supplement affect clotting?" is a real one. This page sets out what the sources we read say. The honest summary is that the evidence is uneven: some supplements have a clear warning, some have conflicting results, and for many there is little or nothing. It is information only, and any change to a prescribed medicine is for the prescriber to decide.

What the main literature review found

A 2022 review in Proceedings (Baylor University Medical Center) searched PubMed for bleeding risks of popular herbal and dietary supplements. It notes these products can potentially alter bleeding and clotting during surgery and when used with anticoagulants. [1] Its findings:

Ginkgo appears in two rows because the review found it linked to bleeding risk in people on anticoagulants while calling the overall evidence conflicting. [1] This is the kind of uncertainty that a clinician or pharmacist can help weigh.

Official statements on single products

• Ginkgo (Ginkgo biloba). NCCIH says ginkgo may increase the risk of bleeding in people taking anticoagulant drugs such as warfarin. [2] See ginkgo.
• Garlic (Allium sativum) supplements. NCCIH says garlic supplements may increase the risk of bleeding. [3] See garlic.
• Feverfew (Tanacetum parthenium). NCCIH says feverfew may slow blood clotting. [4] See feverfew.
• Chamomile (Matricaria chamomilla). NCCIH says interactions between chamomile and warfarin have been reported. [5] See chamomile.
• St. John's wort (Hypericum perforatum). NCCIH lists warfarin among the medicines it can weaken. [6] See St. John's wort interactions.

Fish oil: a case where reviews disagree with the worry

Fish oil is often thought to thin the blood. A 2014 review (British Journal of Nutrition) found n-3 fatty acid treatment had no effect on the risk of clinically significant bleeding, whether used alone or with other treatments. [7] The 2022 review above also found no association with bleeding. [1] Both are reviews, not new trials, and neither tells an individual what is right for them. See fish oil and omega-3 safety.

Bleeding disorders

NIH's 2008 pocket guide for clinicians on von Willebrand disease says to counsel patients to avoid aspirin, other NSAIDs and other platelet-inhibiting drugs. [8] That is about medicines. "Proper evidence not found": we searched the NIH guide, NCCIH pages and the review above for studies of herbs or supplements in people with hemophilia or von Willebrand disease and found none. We cannot say any supplement is safe for them. A hematology team is the right place to ask.

Who should ask first

• People with a bleeding disorder, easy bruising or heavy periods.
• People taking warfarin or other anticoagulants, aspirin or other platelet medicines. See supplements and blood thinners and narrow-range medicines.
• Anyone having surgery or a dental procedure. Tell the surgical and anesthesia teams about every supplement. See supplements before surgery.

Vitamin E and vitamin K are covered in vitamins and blood thinners.