The short answer
The additional bleeding risk from willow bark with pentoxifylline is uncertain. Review the exact product and your bleeding risk factors with your prescriber.
What this answer covers
Oral willow bark products with oral extended-release pentoxifylline. Exact formulation and clinical setting matter; aspirin, warfarin and other medicines are not interchangeable.
- Supplement or preparation
- Willow Bark
- Medication ingredient
- pentoxifylline
What the original evidence shows
The final European willow bark monograph cautions about certain pain medicines and coumarin anticoagulants. Pentoxifylline belongs to neither of those groups, so those warnings cannot by themselves prove this pair increases bleeding. The exact combination has no established bleeding estimate in the inspected evidence.
Pentoxifylline’s own evidence matters
Bleeding has been reported with pentoxifylline, including in people taking other medicines that affect bleeding. However, a small randomized study in patients with diabetes and coronary disease found no extra platelet inhibition when pentoxifylline was added to aspirin and clopidogrel. This does not exclude rare bleeding, but it limits blanket assumptions about additive effects.
Review the actual supplement
Show the willow species, salicin content, dose and other ingredients to your pharmacist. Active ulcer disease is a contraindication in the monograph and also matters in pentoxifylline’s bleeding assessment. Review that personal risk rather than assuming willow is equivalent to aspirin or applying an untested spacing rule.
Use a monitoring plan, not an untested spacing rule
The label recommends assessment for bleeding in people with risk factors such as recent surgery or ulcer disease. Tell your prescriber about unusual bruising, persistent nosebleeds or other new bleeding; substantial or ongoing bleeding needs prompt care. No supplement-specific hours-apart schedule has been shown to prevent these concerns, and you should not change pentoxifylline yourself.
Evidence and practical considerations
Side effects & toxicity
An increased bleeding rate specifically from willow bark with pentoxifylline has not been established.
- Exact scope
- Oral willow bark products with oral extended-release pentoxifylline. Exact formulation and clinical setting matter; aspirin, warfarin and other medicines are not interchangeable. with Exact pentoxifylline RxCUI 8013 IN confirmed by current RxNorm. Oral extended-release 400 mg tablets for intermittent claudication; experimental immediate-release, intravenous and other-drug exposures are distinct.
- Medication form and route
- Oral
What remains uncertain
- Available other-drug, short-duration and surrogate-endpoint findings do not quantify this exact pair’s clinical bleeding risk. No validated protective dose separation.
Factors that may matter: Exact preparation and dose; Fasting versus fed dosing; Bleeding and ulcer history; Other medicines.
Read the supporting source summaries
Source 1: Current prescribing information
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Adults with intermittent claudication due to chronic occlusive arterial disease.
Bleeding reported with or without NSAIDs, anticoagulants or platelet inhibitors. Prior methylxanthine intolerance, including caffeine, is a contraindication. Pentoxifylline can raise theophylline levels; strong CYP1A2 inhibitors can raise pentoxifylline exposure.
How this applies: Exact drug/formulation guidance. Exact pentoxifylline RxCUI 8013 IN confirmed by current RxNorm. Oral extended-release 400 mg tablets for intermittent claudication; experimental immediate-release, intravenous and other-drug exposures are distinct.
Does not establish an interaction with every supplement, or transfer theophylline effects to caffeine. Occasional hypotension/arrhythmia reports were not more frequent than placebo in controlled trials. Immediate-release adverse-event results differ from extended-release.
Source 2: Original clinical research
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 40 evaluable patients with type 2 diabetes and stable coronary artery disease receiving aspirin and clopidogrel.
No additional inhibition across the measured platelet-function assays.
How this applies: Interpret exact preparation, comparator and endpoint; no automatic combination causality.
Abstract-only; publisher body access failed 403. Short surrogate-endpoint study, no herbs and not proof of absence of rare clinical bleeding.
Source 3: Final regulatory herbal monograph
ema.europa.eu · Source check Sep 10, 2026
Population: Users of defined medicinal willow bark preparations.
Cautions with NSAIDs/salicylates and coumarin anticoagulants; active peptic ulcer is a contraindication.
How this applies: Supplement scope and risk-factor context, with class mismatch explicit.
Pentoxifylline is neither an NSAID nor a coumarin. This source does not directly establish the exact combination’s bleeding risk or a spacing rule.
Source 4: Medication terminology
rxnav.nlm.nih.gov · Source check Sep 10, 2026
Population: Terminology.
Pentoxifylline, IN.
How this applies: Exact identity.
Not clinical evidence.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Sources checked and article drafted. | |
| Research summary published |
Article revision: 96b93d8cb0db55ca
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.