The short answer
Yes, there is evidence of an interaction, from a single case. An 80-year-old woman on warfarin had an INR of 5.5 and serious blood loss after eating a large amount of black licorice, and it happened twice.
Licorice may change how a blood thinner works. A high INR raises the risk of bleeding, and a low INR gives less protection against clots. If you take warfarin or acenocoumarol, tell your prescribing doctor before you take mulethi in any form, including licorice sweets, and ask whether your INR should be checked more often.
Warfarin is sold in India as Warf. Acenocoumarol, a related blood thinner, is sold as Acitrom.
At a glance
| What was seen | How it may work | Direction | Evidence |
|---|---|---|---|
| INR of 5.5 and bleeding in a woman on warfarin after black licorice[1] | Not established | Stronger blood-thinning effect; bleeding | Case report |
| Possible faster clearance of warfarin[2] | Liver enzymes switched up; mostly lab and animal data | Warfarin effect could decrease | Theoretical by mechanism |
No listing is not a clearance. A missing interaction here never means a combination is safe.
The evidence, study by study
Case report, 2010 Case report
An 80-year-old woman taking warfarin for atrial fibrillation had two episodes of bleeding into the gut, each after eating about a pound of black licorice. At the latest, her INR was 5.5 against a usual 2.1, and her haematocrit, a measure of red blood cells, had fallen from 34 to 14. Two weeks after she cut out the licorice, her INR was 1.2. The glycyrrhizin in the sweets was not measured, and black licorice can also darken stools.[1]
What your doctor may watch for
- Your INR, with extra tests when you start or stop any herbal product, including licorice.[3]
- Bruising, bleeding or black stools. Licorice can darken stools on its own, but in the 2010 case there was real blood loss.[1]
What to tell your prescribing doctor
You can read this out, or show them this page:
“I am taking, or planning to take, mulethi (licorice) as a tea, powder, sweet, lozenge or cough product (name and how much) along with my blood thinner. A woman on warfarin had a raised INR and bleeding after eating black licorice. Should my INR be checked more often?”
Withheld until review
Questions people ask
Is a little mulethi in cough syrup or tea a concern?
Nobody knows how much is enough to matter. The 2010 case involved a large amount of licorice sweets. Mention any licorice product, however small, when your INR is checked.[1]
Related
Turmeric and blood thinners
Two reports describe a raised INR after turmeric in people on warfarin-type blood thinners. Blood thinners leave little margin.
InteractionTulsi and blood thinners like warfarin
A man on warfarin had a high INR after a herbal kadha that included tulsi. Tulsi's own role is not clear, and it has not been studied alone.
InteractionGinger (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.
InteractionMulethi (licorice) and blood pressure medicines
Glycyrrhizin in mulethi raises blood pressure and lowers potassium. It can work against blood pressure medicines, as a regulator and a case report show.
Sources
- Liu JF, Srivatsa A, Kaul V. Black licorice ingestion: yet another confounding agent in patients with melena. World J Gastrointest Surg. 2010;2(1):30-31. PMID 21160832.
- Memorial Sloan Kettering Cancer Center. About Herbs: Licorice (health professional information, herb-drug interactions).
- Warfarin sodium tablets, US prescribing information (DailyMed).
Updated 4 November 2026
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