Drug & supplement interaction

Onion + Phenprocoumon

Phenprocoumon brand name: Liquamar.

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

Onion has a moderate interaction with Phenprocoumon. Theoretically, concomitant use of anticoagulant or antiplatelet drugs with onion might increase the risk of bleeding.

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

Onion 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 Onion interacts with.

Theoretically, concomitant use of anticoagulant or antiplatelet drugs with onion might increase the risk of bleeding.
In vitro research shows that onion inhibits platelet aggregation.
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 long-acting blood thinner, similar to warfarin, and it's a narrow-therapeutic-index drug. That means even small shifts in how thin your blood is can matter, so this one is worth watching.

Here's the idea behind this interaction: in lab studies, onion compounds appear to make platelets (the cells that help form clots) a little less sticky. Stacking that on top of Phenprocoumon could, in theory, nudge your bleeding risk up. Be honest though, this is theoretical, based on test-tube work, not real patient reports. Normal food amounts of onion in your meals are very unlikely to cause trouble. Concentrated onion supplements are the bigger question mark. Watch for easy bruising, nosebleeds, or bleeding gums, and check with your pharmacist or doctor before starting any onion supplement.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  2. Hubbard, G. P., Wolffram, S., de Vos, R., Bovy, A., Gibbins, J. M., and Lovegrove, J. A. Ingestion of onion soup high in quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in man: a pil

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

Onion Also Interacts With Other Medications

Onion has 274 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 274 No known interaction 2,556 (incl. Phenprocoumon)
Taking anything else?

Check Another of Your Medications Against Onion

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

Everything else you take

See Every Supplement That Interacts With Phenprocoumon

This page covers Onion 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 Onion as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1,061 real supplement products containing Onion, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Onion. Your product may carry other ingredients that interact with Phenprocoumon too, on top of Onion — 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 Onion 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 Onion
Top 25%

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

29 days ago today
Medication Phenprocoumon
Top half

#753 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 Onion

What is Onion?

Onion
  • Colds and respiratory symptoms
  • Heart and cholesterol health
  • Blood sugar support
  • Antimicrobial and wound care
  • Scar appearance (topical gels)

Onion is a common food with a long history in traditional medicine, and it contains antioxidants like quercetin and sulfur compounds. Eating onion as part of a balanced diet is safe for most people, but high-dose supplements have only limited human evidence for any specific health condition. Talk with your pharmacist or doctor before using concentrated onion products for a medical reason.

Read the full Onion monograph & all interactions
Keep checking

Other Drugs & Onion

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

0Major
274Moderate
0Minor
2,555No known interaction
274 Moderate 2,555 No interaction
Moderate

274 interactions

Showing 60 of 274 moderate interactions — see all 274 on the Onion page.

No interaction 2,555 drugs checked — show the list

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

Showing the 60 most looked-up of 2,555 medications checked with no known interaction — see the full Onion list.

See the full Onion 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
Onion 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 Onion and Phenprocoumon Together: Common Questions

Can you take Onion 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 Onion 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 Onion?

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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.