The short answer
Ask your prescriber before taking willow bark with valproate, especially if you have low platelets, unusual bruising or a bleeding disorder. Willow has limited evidence of effects on platelet function, while valproate can affect platelets and clotting. A higher bleeding rate from this exact combination has not been established.
What this answer covers
Oral willow bark medicinal preparations containing salicin. Salicin is not treated as aspirin, and results from a studied extract are not automatically assigned to all Salix products.
- Supplement or preparation
- Willow Bark
- Medication ingredient
- valproate
What the willow study found
A small study compared willow bark extract with placebo in back-pain patients and also examined a separate group taking aspirin. Some platelet responses differed with willow, but its effect was much smaller than aspirin, and the authors said the clinical relevance needed further study.
Why your platelet history matters
Valproate can cause low platelet counts and other clotting abnormalities. The European willow monograph lists coagulation disorders as a reason not to use its specified preparations. Report new bruising or bleeding to your treating team, particularly before adding willow.
Willow is not an aspirin substitute in the evidence
The label reports that aspirin affected free valproate levels in a small pediatric study. Willow contains salicin, and that aspirin finding does not show the same effect from willow bark. Do not use it to calculate an equivalent willow dose.
Review use rather than relying on spacing
The sources do not establish a spacing interval that prevents a willow-valproate problem. Bring your willow label and all medicines to a pharmacist or prescriber, especially if you already have a bleeding disorder or abnormal blood counts.
Evidence and practical considerations
Side effects & toxicity
Limited willow platelet findings and valproate-associated coagulation problems support review, especially with existing bleeding problems; pair-specific bleeding and timing effects remain unknown.
- Exact scope
- Oral willow bark medicinal preparations containing salicin. Salicin is not treated as aspirin, and results from a studied extract are not automatically assigned to all Salix products. with Oral valproate active moiety; label evidence is from oral valproic acid capsules, with Depakote exposure identified separately where relevant.
- Medication form and route
- oral valproate; supplement route as specified in source and scope
- Timing or duration
- No safe co-use duration or protective spacing interval established.
What remains uncertain
- Laboratory outcomes do not establish clinical bleeding. The aspirin comparator involved a separate population, and the valproate aspirin interaction cannot be assigned to salicin.
Factors that may matter: low platelet count; coagulation disorder; other medicines affecting bleeding.
Read the supporting source summaries
Source 1: current oral product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed oral valproic acid capsules.
Label warns of potentially fatal liver injury, especially during the first six months, and thrombocytopenia/coagulation abnormalities. It recommends baseline and follow-up liver and blood assessments. P450 oxidation is a minor metabolic pathway. Aspirin increased free valproate fraction in six pediatric patients; the study is aspirin-specific.
How this applies: Medication risk and identity context for RxCUI 40254 valproate; oral active-moiety bridge only.
Not a study of any of these botanical combinations. Active-moiety identity does not establish interchangeable doses, release kinetics or routes. Aspirin results do not establish salicin or methyl salicylate effects.
Source 2: controlled platelet-aggregation study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 35 low-back-pain patients randomized to willow extract (19) or placebo (16), plus a separate group of 16 ischemic-heart-disease patients taking aspirin.
Some laboratory platelet-aggregation responses were lower with willow than placebo, but effects were much smaller than with aspirin. No difference was found with collagen stimulation; clinical relevance remained uncertain.
How this applies: Limited reason for caution when platelet function is impaired; does not establish aspirin-equivalent effects, valproate concentration changes or pair-specific bleeding.
No valproate co-use or clinical bleeding outcome. Aspirin group was a separate population, not a third randomized arm. Exact Salix species and preparation generalizability limited by abstract.
Source 3: EMA herbal monograph or public assessment summary
ema.europa.eu · Source check Sep 10, 2026
Population: People considering the specified herbal medicinal preparations.
Coagulation disorders are contraindications for the specified willow preparations. Salicin metabolism and limited platelet-aggregation effects are described.
How this applies: Supports assessing existing coagulation problems before oral willow use; does not show aspirin-equivalent effects.
No direct valproate trial. A coumarin-anticoagulant warning cannot be treated as direct evidence for valproate.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Original sources checked and exact-pair evidence package prepared; no clinical review asserted. | |
| Research summary published |
Article revision: 66a68234135721e5
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.