What herbal supplements increase the risk of blood clots?

Herbal Supplements That Increase the Risk of Blood Clots

Several herbal supplements should be discontinued at least 2 weeks before surgery due to their potential to increase bleeding risk by affecting platelet function and coagulation pathways. 1

Key Herbs That Increase Bleeding Risk

Strong Evidence for Bleeding Risk

• Feverfew, garlic, ginkgo biloba, ginger, and ginseng - May alter bleeding time and should not be used with warfarin 1
• St. John's Wort - Can enhance warfarin metabolism, reducing its effectiveness 1
• Turmeric/Curcumin - Inhibits platelet aggregation and prolongs activated partial thromboplastin time 1
• Ginger - Contains constituents with antiplatelet effects in vitro; case reports show elevated INR and epistaxis 1

Moderate Evidence for Bleeding Risk

• Saw palmetto - May increase bleeding time leading to hematuria and operative bleeding 1
• Fenugreek - Aqueous extracts inhibit coagulation and significantly prolong prothrombin time 1
• Flaxseed oil - Decreases platelet aggregation in healthy individuals 1
• Green tea extract - Active ingredient EGCG inhibits platelet aggregation 1
• Moringa - Interacts with warfarin and other blood thinners 2

Mechanism of Action

These herbal supplements increase bleeding risk through several mechanisms:

1. Platelet inhibition - Herbs like ginkgo biloba, garlic, and green tea inhibit platelet aggregation 1, 3
2. Coagulation cascade interference - Turmeric and fenugreek prolong prothrombin time and activated partial thromboplastin time 1
3. Interaction with anticoagulants - St. John's Wort reduces the effectiveness of warfarin through enhanced metabolism 1
4. Direct thrombin inhibition - Some herbs contain compounds that directly inhibit thrombin formation 1

Clinical Recommendations

Preoperative Management

1. Discontinuation timing: All herbal medicines should be discontinued 2 weeks before surgery 1, 4
2. Patient screening: Specifically inquire about herbal supplement use during preoperative assessment 4
3. High-risk patients: Those on anticoagulants should be advised to avoid these supplements entirely 1

Special Considerations

• Ginkgo biloba: Despite some conflicting evidence 5, guidelines recommend discontinuation before surgery due to case reports of spontaneous bleeding 6
• Fish oil: Large placebo-controlled trials show no increase in perioperative bleeding, but caution is still advised 1
• Combination risk: Risk increases when multiple supplements are used together or with conventional anticoagulants 6

Common Pitfalls and Caveats

1. Lack of disclosure: Patients often don't report supplement use to healthcare providers 6
2. Inconsistent manufacturing: Herbal supplements lack standardization, leading to variable potency and effects 2
3. Delayed effects: Some herbs may affect coagulation for days to weeks after discontinuation 4
4. False sense of safety: "Natural" products are often perceived as harmless by patients 4
5. Conflicting evidence: For some supplements like ginkgo biloba and cranberry, evidence of bleeding risk is mixed 6

When in doubt about a specific herbal supplement's bleeding risk, the safest approach is to recommend discontinuation at least 2 weeks before any surgical procedure or when starting anticoagulant therapy.