Drug & supplement interaction

Willow Bark + Dalteparin

Dalteparin brand name: Fragmin.

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

Willow Bark has a moderate interaction with Dalteparin. Theoretically, willow bark might increase the risk of bleeding when taken with anticoagulant/antiplatelet drugs.

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

Willow Bark and Dalteparin

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

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

Why this applies to Dalteparin

Dalteparin falls under ANTICOAGULANT/ANTIPLATELET DRUGS — the group Willow Bark interacts with.

Theoretically, willow bark might increase the risk of bleeding when taken with anticoagulant/antiplatelet drugs.
Willow bark has antiplatelet effects, but less so than aspirin.
Severity Moderate Likelihood Probable Evidence D

Interaction 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..

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

Here's the situation: dalteparin (Fragmin) is an injectable blood thinner that lowers your blood's ability to clot. Willow bark contains salicin, which your body turns into a substance that works a lot like aspirin and gently discourages platelets from sticking together. Stack those two together and you're hitting your clotting system from two different angles, so theoretically the bleeding risk goes up a bit.

In real life that might look like easier bruising, nosebleeds, bleeding gums, or longer bleeding from a small cut. I'll be honest with you though: this concern is based on how willow bark works, not on strong studies, and its blood-thinning effect is milder than aspirin's. Still, since dalteparin is already a serious blood thinner, please check with your pharmacist or doctor before adding willow bark.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Krivoy N, Pavlotzky E, Chrubasik S, et al. Effect of salicis cortex extract on human platelet aggregation. Planta Med 2001;67:209-12. 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

Willow Bark Also Interacts With Other Medications

Willow Bark has 126 moderate known drug interactions in our database — the Dalteparin one above is one of them. If you take anything else, check it against the full list below.

Moderate 126 No known interaction 2,704 (incl. Dalteparin)
Taking anything else?

Check Another of Your Medications Against Willow Bark

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

Everything else you take

See Every Supplement That Interacts With Dalteparin

This page covers Willow Bark only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dalteparin page lists 218 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), Aconite (moderate) and Allspice (moderate).

By severity: 3 major · 190 moderate · 25 minor.

From our pharmacist’s overview on the Dalteparin page

“Dalteparin (Fragmin) is an injectable blood thinner used to prevent and treat dangerous clots, which is exactly why this list warrants real vigilance, and nearly all 218 ingredients on it thin the blood too. They are herbs and extracts with clot-inhibiting or antiplatelet effects of their own, so stacking them on dalteparin can push bl…”

Reviewed by 2 · Jul 18, 2026

Open the Dalteparin interaction page

One more smart check

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

We hold 43 real supplement products containing Willow Bark, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Willow Bark. Your product may carry other ingredients that interact with Dalteparin too, on top of Willow Bark — 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 Willow Bark and Dalteparin 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 Willow Bark
Steady interest

#1,187 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Dalteparin
Top half

#884 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 Willow Bark

What is Willow Bark?

  • Low back pain
  • Osteoarthritis joint pain
  • Headache
  • Fever
  • General aches and inflammation

Willow bark is a traditional plant remedy that contains salicin, a compound related to aspirin, and is most often used for pain and inflammation. Some evidence suggests it may modestly help low back pain and joint pain, but the research is limited and the right dose is not well standardized. Because it acts like aspirin, people with aspirin allergies, bleeding problems, or who are pregnant should be cautious and talk to a pharmacist or doctor first.

Read the full Willow Bark monograph & all interactions
Medication

About Dalteparin Injection

What Is Dalteparin Injection Used For?

Brand name: Fragmin

Fragmin (dalteparin) injection is used to prevent blood clots (deep vein thrombosis, or DVT) in people having hip replacement or abdominal surgery, and in hospitalized patients who are largely immobile due to acute illness. It is also used to reduce ischemic complications — meaning clot-related events — in people with unstable angina or a type of heart attack called non-Q-wave MI, when given alongside aspirin.

Fragmin is approved for the extended treatment of symptomatic venous thromboembolism (VTE — blood clots in the veins or lungs) in adults with cancer, to reduce the chance of clots coming back, for up to six months. It is also approved to treat symptomatic VTE in pediatric patients from birth (at least 35 weeks gestational age) onward. Fragmin is not intended for the acute (immediate emergency) treatment of VTE.

See full Dalteparin Injection drug information
Keep checking

Other Drugs & Willow Bark

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

0Major
126Moderate
0Minor
2,703No known interaction
126 Moderate 2,703 No interaction
Moderate

126 interactions

Showing 60 of 126 moderate interactions — see all 126 on the Willow Bark page.

No interaction 2,703 drugs checked — show the list

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

Showing the 60 most looked-up of 2,703 medications checked with no known interaction — see the full Willow Bark list.

See the full Willow Bark interactions page
See every supplement checked against Dalteparin, 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
Willow Bark monograph › Uses, safety, and every drug interaction in one place Dalteparin supplement interactions › Every supplement checked against Dalteparin, ranked by severity Dalteparin Injection drug information › The full plain-English guide to this medication 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 Willow Bark and Dalteparin Together: Common Questions

Can you take Willow Bark with Dalteparin?
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 Willow Bark and Dalteparin 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 Dalteparin and Willow Bark?

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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.