Short answer: It is not clear-cut. The NIH LactMed record says turmeric may increase the risk of bleeding in people taking warfarin and antiplatelet drugs, and lab studies show turmeric can reduce platelet clumping. But a small 10-day study of one curcumin product found no change in bleeding time or INR. Products also vary widely, so the prescriber or pharmacist should know before you start.
LactMed, the NIH (NICHD) database on medicines and breastfeeding, says in its turmeric record that turmeric "may increase the risk of bleeding in patients taking warfarin and antiplatelet drugs."
A 2015 review of herbs and blood clotting (McEwen) lists turmeric among herbs that reduced platelet aggregation, the clumping that starts a clot, in lab (in vitro) studies. It also says that for people on warfarin, clotting tests may need repeating after herbal medicines are stopped. Lab findings show a possible effect; they do not show how much it matters in people.
Hu 2018 tested a curcumin product (Meriva) in people already on blood thinners. After 10 days:
| Medicine | Measure | Result |
|---|---|---|
| Aspirin, ticlopidine or clopidogrel | Bleeding time | No significant change |
| Warfarin or dabigatran | INR | No significant change |
The study was short, small and tested one formulation, so it cannot rule out an effect with other products, higher amounts or longer use.
Turmeric is a plant in the ginger family. The NCCIH says its effects are usually credited to curcuminoids, including curcumin, the compound that gives the spice its yellow color. It also says oral curcumin products vary in how much curcumin they actually contain and often include substances from other plants, such as piperine from black pepper, which is added to increase absorption. That makes results from one product hard to apply to another.
The NCCIH also says conventional turmeric or curcumin is likely safe in recommended amounts for up to 2 or 3 months, can cause nausea, reflux, diarrhea or constipation, and that liver damage has been reported with some high-absorption curcumin products. It advises talking with a provider before using any herbal product if you take medicine, because some herbs and medicines interact.
Turmeric as a cooking spice is different from a concentrated supplement. Useful details for the prescriber or anticoagulation clinic are the product name, the curcumin amount per capsule, whether it has black pepper extract, and when you started. If you take warfarin, an INR change soon after starting or stopping a supplement is worth flagging.
Other supplements raise similar questions; see fish oil and blood thinners and vitamin E and blood thinners. Dose Track can log supplements next to prescriptions, so the start date is on hand when a lab result shifts.
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