Drug & supplement interaction

Garlic + Phenprocoumon

Phenprocoumon brand name: Liquamar.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Garlic has a moderate interaction with Phenprocoumon. Garlic may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Garlic and Phenprocoumon

Here is the interaction we found between these two, with the evidence behind it.

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

Why this applies to Phenprocoumon

Phenprocoumon falls under ANTICOAGULANT/ANTIPLATELET DRUGS — the group Garlic interacts with.

Garlic may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Raw garlic and a variety of garlic extracts have antiplatelet activity and can increase prothrombin time.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Phenprocoumon is a blood thinner that works a lot like warfarin, keeping your blood from clotting too easily. Garlic, especially in concentrated supplement form, can have its own mild blood-thinning action by making your platelets a little less sticky. When you stack these two together, the effects can add up and nudge your bleeding risk higher. That could show up as easy bruising, nosebleeds, bleeding gums, or blood that takes longer to stop.

I'll be honest with you: this concern is based mostly on how garlic works in the lab, not on strong patient studies, so the real-world risk is likely small. Everyday garlic in your cooking is generally no worry. Still, because phenprocoumon is a finicky drug where small shifts matter, please check with your pharmacist or doctor before starting a garlic supplement.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Rose KD, Croissant PD, Parliament CF, Levin MB. Spontaneous spinal epidural hematoma with associated platelet dysfunction from excessive garlic ingestion: a case report. Neurosurg 1990;26:880-2. PubMed
  2. Sunter WH. Warfarin and garlic. Pharm J 1991;246:722.
  3. Steiner M, Lin RS. Changes in platelet function and susceptibility of lipoproteins to oxidation associated with administration of aged garlic extract. J Cardiovasc Pharmacol 1998;31:904-8. PubMed
  4. Rahman K, Billington D. Dietary supplementation with aged garlic extract inhibits ADP-induced platelet aggregation in humans. J Nutr 2000;130:2662-5. PubMed
  5. Steiner M, Li W. Aged garlic extract, a modulator of cardiovascular risk factors: a dose-finding study on the effects of AGE on platelet functions. J Nutr 2001;131:980S-4S. PubMed
  6. Kiesewetter H, Jung F, Jung EM, et al. Effect of garlic on platelet aggregation in patients with increased risk of juvenile ischaemic attack. Eur J Clin Pharmacol 1993;45:333-6. PubMed
  7. Legnani C, Frascaro M, Guazzaloca G, et al. Effects of a dried garlic preparation on fibrinolysis and platelet aggregation in healthy subjects. Arzneimittelforschung 1993;43:119-22.
  8. Gadkari JV, Joshi VD. Effect of ingestion of raw garlic on serum cholesterol level, clotting time and fibrinolytic activity in normal subjects. J Postgrad.Med 1991;37:128-131.
  9. Woodbury A, Sniecinski R. Garlic-induced surgical bleeding: How much is too much? A Case Rep. 2016;7(12):266-269. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Garlic Also Interacts With Other Medications

Garlic has 988 moderate known drug interactions in our database — the Phenprocoumon one above is one of them. If you take anything else, check it against the full list below.

Moderate 988 No known interaction 1,842 (incl. Phenprocoumon)
Taking anything else?

Check Another of Your Medications Against Garlic

Covers the 2,830 medications we’ve checked against Garlic. Pick one to open its full report.

From our Q&A

Questions About Garlic or Phenprocoumon

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Garlic or Phenprocoumon, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Phenprocoumon

This page covers Garlic only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Phenprocoumon page lists 219 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Danshen (major), Piracetam (major), St. John's Wort (major) and Aconite (moderate).

By severity: 4 major · 190 moderate · 25 minor.

From our pharmacist’s overview on the Phenprocoumon page

“Phenprocoumon (Liquamar) is a blood thinner in the coumarin family, a close cousin of warfarin, and small shifts in its blood level can tip you toward a clot or a bleed, so I treat this list with genuine care. Almost everything on it pushes the drug's effect further, layering extra bleeding risk on blood that is already thinned.”

Reviewed by 2 · Jul 18, 2026

Open the Phenprocoumon interaction page

One more smart check

Taking Garlic as Part of a Dietary Supplement Product? Check It for Interactions

We hold 4,118 real supplement products containing Garlic, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Garlic. Your product may carry other ingredients that interact with Phenprocoumon too, on top of Garlic — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Garlic and Phenprocoumon Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Garlic
Top 5%

#59 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Phenprocoumon
Top half

#781 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Garlic

What is Garlic?

Garlic
  • High blood pressure
  • High cholesterol
  • Heart health
  • Immune support and common cold
  • Antimicrobial uses

Garlic is a common food and supplement that may modestly help with blood pressure and cholesterol, though the evidence is mixed and effects are usually small. It is generally safe in food amounts, but concentrated supplements can cause stomach upset, breath and body odor, and a higher risk of bleeding. Talk with your pharmacist or doctor before taking garlic supplements, especially if you take other medicines.

Read the full Garlic monograph & all interactions
Keep checking

Other Drugs & Garlic

Browse every other medication we’ve checked against Garlic — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
988Moderate
0Minor
1,841No known interaction
988 Moderate 1,841 No interaction
Moderate

988 interactions

Showing 60 of 988 moderate interactions — see all 988 on the Garlic page.

No interaction 1,841 drugs checked — show the list

We also checked Garlic against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,841 medications checked with no known interaction — see the full Garlic list.

See the full Garlic interactions page
See every supplement checked against Phenprocoumon, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Garlic monograph › Uses, safety, and every drug interaction in one place Phenprocoumon supplement interactions › Every supplement checked against Phenprocoumon, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Garlic and Phenprocoumon Together: Common Questions

Can you take Garlic with Phenprocoumon?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Garlic and Phenprocoumon interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Phenprocoumon and Garlic?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.