The short answer

Mixing herbal supplements with blood thinners is a common reason people end up with unexpected bruising, nosebleeds, or unstable lab results.

Even when a product is labeled “natural,” it can still change how your blood clots or how your liver processes medications. Pharmacists and anticoagulation clinics routinely caution against “stacking” herbs with anticoagulants or antiplatelet drugs, especially if you are taking more than one medication that affects bleeding.

The risk is not the same for everyone. It depends on which blood thinner you take (for example, warfarin versus a direct oral anticoagulant), your kidney and liver function, your age, and whether you have had a prior bleeding event.

Important: Do not stop your blood thinner on your own because you are worried about an herb. Stopping suddenly can raise the risk of a dangerous clot. Contact your prescriber or anticoagulation clinic for individualized advice.

Why herbs and blood thinners can be a risky mix

There are two main ways herbs can cause problems.

First, some herbs have their own blood thinning effects. They may reduce platelet “stickiness,” affect clotting factors, or change blood vessel behavior. When combined with a prescribed blood thinner, the effects can add up.

Second, some herbs alter drug metabolism and transport. Many medications are processed by liver enzymes and transported by proteins that move drugs in and out of cells. If an herb speeds up or slows down these pathways, your blood thinner level can become too high (bleeding risk) or too low (clot risk).

Warfarin deserves special caution because its effect is sensitive to changes in diet, illness, alcohol, and supplements. Many clinicians consider warfarin the most interaction-prone anticoagulant, and they often recommend avoiding nonessential supplements unless your care team is monitoring closely.

Herbs and supplement ingredients that commonly raise concern

Not every herb interacts, but these are frequently flagged by clinicians because of reported bleeding, lab changes, or plausible mechanisms.

St. John’s wort: This is a higher-risk one because it can make some medications less effective by increasing drug breakdown. If your blood thinner level drops, your clot risk can rise, even if you feel fine.

Ginkgo biloba: Often used for memory, it may increase bleeding tendency, particularly when combined with other blood-thinning agents. People sometimes notice easier bruising first.

Garlic supplements (high-dose): Culinary garlic in food is usually not the issue, but concentrated pills and extracts can have stronger antiplatelet effects. The risk is higher if you also take aspirin, clopidogrel, or NSAIDs.

Ginseng: Some forms may affect clotting and can also interfere with warfarin control in some people. Effects can be unpredictable between products.

Turmeric and curcumin (high-dose): These are popular for inflammation, but concentrated doses may increase bleeding risk in susceptible people. This is different from using turmeric as a spice in normal amounts.

Danshen, dong quai, and other traditional herbal blends: Multi-ingredient products are challenging because interactions can come from one component, and labels may not list standardized amounts.

A special note on “omega” and “vitamin” products: fish oil and vitamin E are sometimes discussed as increasing bleeding tendency at higher supplemental doses. Vitamin K can counteract warfarin in a dose-dependent way. Your clinician may not tell you to avoid vitamin K entirely, but they often recommend consistency and monitoring if you use it.

Who should be especially cautious

Some situations make the safety margin much smaller.

If you take warfarin: Most guidelines and clinical practice resources recommend extra caution with new supplements because warfarin response can swing with relatively small changes. Your care team may want an extra INR check after any change.

If you have kidney or liver disease: Drug clearance can be reduced, so “normal” doses of a blood thinner can act stronger. Adding an herb that also affects clotting can tip you into bleeding.

If you are older, have a history of falls, or have had a prior bleed: Your baseline risk is higher, so even modest additive effects matter.

If you take more than one agent that affects bleeding: Examples include a blood thinner plus aspirin, clopidogrel, or frequent NSAID use. The combination is sometimes medically necessary, but it raises bleeding risk, and herbs can add another layer.

If you are pregnant or postpartum: Anticoagulation choices differ in pregnancy, and some herbs are not recommended in pregnancy at all. This is a “check first” scenario.

If any of these apply, it is generally recommended to avoid starting herbal supplements unless your clinician explicitly agrees and has a monitoring plan.

How to lower your risk if you still want to use an herb

Some people take supplements for pain, sleep, anxiety, or “immune support.” If you are on a blood thinner, the safest approach is to treat any supplement like a medication change.

Start by writing down exactly what you plan to take, including the brand, dose, and how often. “Turmeric” can mean a spice, a 500 mg capsule, or a high-potency extract with added ingredients.

Then use these steps:

Ask your pharmacist to check interactions with your exact blood thinner and medication list. This is often faster than a clinic visit, and pharmacists can look for both bleeding risk and metabolism interactions.

Avoid multi-ingredient blends when possible. A single-ingredient product is easier to evaluate, and it is easier to stop if you develop symptoms.

Do not “cycle” doses without telling your care team. Taking an herb only on workout days, travel days, or “when you remember” can create fluctuating anticoagulation effects, especially with warfarin.

Choose non-supplement options for the same goal when you can. For inflammation or cardiometabolic health, a food-first approach such as Anti-inflammatory Foods is usually easier to manage safely than concentrated extracts.

Pro Tip: Bring your supplement bottles (or clear photos of the labels) to appointments. Many interactions come from added ingredients, like black pepper extract (piperine), that are easy to miss when you only list the main herb.

Warning signs, when to stop, and when to seek urgent care

If you and your clinician decide an herb is acceptable, you still need a plan for what to watch for.

Call your clinician promptly if you notice:

New or worsening bruising, frequent nosebleeds, or bleeding gums. These can be early signs that your blood is “too thin,” especially if they are new for you.

Black, tarry stools or red blood in stool or urine. These can signal internal bleeding and should be assessed urgently.

Severe headache, sudden weakness, confusion, or trouble speaking. These are emergency symptoms because bleeding in the brain is possible, particularly if you are over-anticoagulated.

Sudden chest pain, shortness of breath, one-sided leg swelling, or sudden vision changes. These can be signs of a clot if your blood thinner effect has dropped.

If you are taking warfarin and you start any supplement without realizing it could interact, contact your anticoagulation clinic. They may recommend an earlier INR check, even if you feel well.

As you think about overall risk, remember that bleeding risk is also influenced by alcohol intake, dehydration, acute illness, and changes in diet. If you are also managing blood sugar, patterns like the Dawn Effect can tempt people to add supplements for “metabolic support,” but it is safer to discuss those goals with your clinician first.

Key takeaways

Herbal supplements can increase bleeding risk or reduce the effectiveness of blood thinners through additive clotting effects or changes in drug metabolism.

Warfarin is generally considered the most interaction-prone blood thinner, but direct oral anticoagulants can also be affected, especially by herbs that change drug breakdown.

High-risk situations include older age, prior bleeding, kidney or liver disease, and taking multiple medications that affect bleeding.

If you want to use an herb, involve your prescriber or pharmacist first, use single-ingredient products, and have a clear monitoring plan and symptom checklist.

Herbal Supplements and Blood Thinners: Safety Guide

Summary