The short answer
Possibly. The US agency NCCIH warns that garlic supplements may increase the risk of bleeding. Memorial Sloan Kettering's herb guide says garlic may strengthen blood thinners, because it helps the body break down clots and makes platelets, the cells that start a clot, less likely to clump. Aspirin and clopidogrel also work on platelets.
Two small studies found no effect: a single warfarin dose in 12 healthy men, and a 12-week trial of one aged garlic extract in 48 closely watched people on warfarin. Neither can rule out rarer bleeding, and we found no study of garlic with clopidogrel. If you take a blood thinner, tell your prescribing doctor before you start garlic supplements.
Warfarin is sold in India as Warf and low-dose aspirin as Ecosprin. Acitrom (acenocoumarol) is a related blood thinner.
At a glance
| What was seen | How it may work | Direction | Evidence |
|---|---|---|---|
| Bleeding risk warning; less platelet clumping and faster clot breakdown[1][2] | Less platelet aggregation; more fibrinolysis | May add to warfarin, aspirin or clopidogrel | Theoretical by mechanism |
| Heavy bleeding during spinal surgery in a man eating a lot of garlic, on no blood thinner[3] | Less platelet clumping (suspected) | Bleeding with garlic alone; could add to blood thinners | Case report |
| No increase in bleeding over 12 weeks in 48 monitored warfarin patients (one aged garlic extract)[4] | None detected | No effect seen; too small to rule out uncommon bleeding | RCT |
| No change in warfarin levels, INR or platelet clumping after two weeks of garlic (single warfarin dose, 12 healthy men)[5] | None detected | No effect seen in this small study | Small clinical study |
No listing is not a clearance. A missing interaction here never means a combination is safe.
The evidence, study by study
Case report, United States, 2016 Case report
A man bled heavily during surgery to decompress and fuse his spine, with no clear source. He said he took no blood-thinning medicines, but in the days before surgery he had eaten the equivalent of about 12 g of garlic a day. The bleeding was controlled with medicines that help clotting. This is one person, on garlic alone, so it shows what garlic can do to bleeding, not a measured interaction with warfarin.[3]
Placebo-controlled pilot trial in people on warfarin, 2006 RCT
Fifty-two people on warfarin were randomised to aged garlic extract (5 mL twice a day) or placebo for 12 weeks, and 48 finished. No increase in bleeding was found, and minor side effects were similar in both groups. The trial tested one aged extract in patients who were closely monitored, and it was too small to rule out uncommon bleeding.[4]
Crossover study in healthy men, 2008 Small clinical study
Twelve healthy men took a single 25 mg dose of warfarin on its own, after two weeks of garlic, and after two weeks of cranberry, in random order. Garlic did not change warfarin levels, INR, clotting factors or platelet clumping, while cranberry raised the INR. One warfarin dose in healthy men says little about months of treatment in patients, and the garlic product is not described in the summary.[5]
What your doctor may watch for
- INR, especially when you start or stop garlic supplements. The warfarin label says it has a narrow therapeutic range and asks for extra checks when botanical products are started or stopped.[6]
- Unusual bruising or bleeding. A normal INR does not measure how well aspirin or clopidogrel are working on platelets.[6]
What to tell your prescribing doctor
You can read this out, or show them this page:
“I take a blood thinner (name and dose), and I am taking, or planning to take, garlic (capsules, oil, extract or raw cloves, and how much). Garlic supplements may increase bleeding risk. Should my INR be checked more often, and which signs of bleeding should I report?”
Withheld until review
Questions people ask
Related
Ginger (adrak) and warfarin
Two women on blood thinners had a high INR after ginger supplements, and ginger users on warfarin reported more bleeding. One small study found no change.
InteractionFenugreek (methi) and warfarin
One reported case of a raised INR on warfarin with methi and another herb, boldo. Warfarin leaves little margin for change.
InteractionTurmeric and blood thinners
Two reports describe a raised INR after turmeric in people on warfarin-type blood thinners. Blood thinners leave little margin.
InteractionGarlic (lahsun) and blood pressure medicines
Aged garlic extract lowered blood pressure further in people already on BP medicines whose pressure was still high. It adds to the drugs' effect.
Sources
- NCCIH (US National Center for Complementary and Integrative Health). Garlic: Usefulness and Safety.
- Memorial Sloan Kettering Cancer Center. About Herbs: Garlic, herb-drug interactions.
- Woodbury A, Sniecinski R. Garlic-induced surgical bleeding: how much is too much? A A Case Rep. 2016;7(12):266-269. PMID 27782907.
- Macan H, Uykimpang R, Alconcel M, Takasu J, Razon R, Amagase H, Niihara Y. Aged garlic extract may be safe for patients on warfarin therapy. J Nutr. 2006;136(3 Suppl):793S-795S. PMID 16484565.
- Mohammed Abdul MI, Jiang X, Williams KM, Day RO, Roufogalis BD, Liauw WS, Xu H, McLachlan AJ. Pharmacodynamic interaction of warfarin with cranberry but not with garlic in healthy subjects. Br J Pharmacol. 2008;154(8):1691-1700. PMID 18516070.
- Warfarin sodium tablets, US prescribing information, sections 2.4 and 7.5 (DailyMed).
Updated 4 November 2026
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