Willow bark
Pronunciation: pronunciation varies by local usage.
- Generic name
- willow bark
- Drug class
- Herbal dietary supplement; salicin-containing bark extract
- Form
- Oral dietary supplement; specific commercial dosage forms were not established in the sources reviewed.
- Route
- Oral
- Legal status
- Over-the-counter dietary supplement in the sources reviewed; country-specific legal-status variation was not established.
Availability and supply rules vary by country
Trade names by country: United States · United Kingdom · Canada
Australia: · Full directory
What willow bark is and how it works
Willow bark is a herbal dietary supplement prepared from the bark of Salix species (e.g., white willow). It contains salicin, a compound chemically related to aspirin, and has been used traditionally to relieve pain and reduce fever. Modern supplement uses focus on short-term relief of lower back pain and other mild to moderate pain. (1) (2)
Willow bark is available over-the-counter as an oral supplement. Heavy-metal contamination (dependent on the bark source) is a recognised safety concern; product-testing and consumer-verification guidance were not established in the sources reviewed for this article. Willow bark is not recommended for children, during pregnancy or breastfeeding, or for people with aspirin/salicylate allergy. Long-term safety data beyond 8 weeks are lacking, and treatment is generally limited to no more than 4 weeks in the monographs reviewed. A healthcare professional should be consulted before use, especially if you take blood-thinning medicines or have a bleeding disorder.
Mechanism of action: how willow bark works
Salicin is the primary active constituent of willow bark; the bark also contains flavonoids and tannins. The USP safety review describes willow bark as having a broader mechanism of action than aspirin alone and, per the literature it reviewed, characterises it as devoid of the serious adverse events associated with aspirin — this is a literature characterisation from the reviewed source, not an independently confirmed clinical safety guarantee, particularly for long-term use or at-risk populations. (1) (2)
What willow bark is used for
Temporary pain relief (e.g., lower back pain)
Monographs such as ESCOP and the British Herbal Compendium describe use of willow bark extract (standardised to 15% salicin) for short‑term management of lower back pain. Clinical studies have used daily salicin doses of 120–240 mg for up to 8 weeks. Broader traditional use also includes relief of mild to moderate pain. (1) (2)
Fever reduction
Historically, willow bark preparations have been used to lower fever. This use is based on traditional practice; supporting modern clinical trial data specific to willow bark for fever are limited. (1)
Before taking willow bark
Do not take / not appropriate for
- A known allergy or sensitivity to aspirin or other salicylates is a reason to avoid willow bark, because anaphylactic reactions are possible; discuss with a healthcare professional. (all products) (1)
- Willow bark is not recommended for children or adolescents, especially during or after viral illnesses, because of the potential risk of Reye syndrome (a class-level concern for salicylate-containing products); discuss with a healthcare professional. (all products) (2)
- Willow bark is not recommended during pregnancy or while breastfeeding, as salicylates cross the placenta and are eliminated slowly in newborns. The USP recommends a cautionary label statement: “Not for use in … women who are pregnant or nursing.” Discuss with a healthcare professional. (all products) (1) (2)
- Combining willow bark with aspirin, other salicylate medicines, or anticoagulant/antiplatelet drugs may add to blood-thinning effects and increase bleeding risk; discuss any such combination with a healthcare professional before use. (all products) (2)
Tell your clinician about
- All prescription and over-the-counter medicines you are taking, especially anticoagulant or antiplatelet medicines, aspirin, or other salicylate-containing products.
- Any bleeding disorder or vulnerability to bleeding.
- If you are pregnant, planning pregnancy, or breastfeeding.
- Any known allergy to aspirin or salicylates.
- If you have concerns about the purity or source of the supplement; product-testing guidance was not established in the sources reviewed for this article.
How to take willow bark
- Take willow bark orally exactly as directed on the product label. Doses are commonly based on extracts standardised to salicin content (e.g., 15% salicin).
- Do not exceed the recommended daily intake. In the monograph dosing context reviewed (short-term treatment of conditions such as lower back pain), treatment duration is typically limited to 4 weeks; a universal duration limit across all willow-bark uses and products was not established in the sources reviewed.
- Food-interaction and stomach-tolerability administration guidance were not established in the sources reviewed for this article; follow the specific product instructions and consult a healthcare professional if you experience stomach upset.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
No specific missed‑dose instruction was found in the reviewed sources. Follow the product label. Do not take an extra dose to make up for a missed one without consulting a healthcare professional.
Overdose
Specific overdose thresholds and management guidance for willow bark were not established in the sources reviewed for this article. As with any substance, if you suspect an overdose or accidental large ingestion, treat it as a potential medical emergency: seek immediate medical attention or contact emergency services. (1)
Side effects
The sources reviewed report gastrointestinal adverse effects and a few allergic reactions in clinical studies using 120-240 mg salicin daily for up to 8 weeks; long-term safety data beyond 8 weeks are absent.
Gastrointestinal upset
What to notice: Specific symptom detail was not established in the sources reviewed for this article; the sources support that gastrointestinal adverse effects have been reported.
What to do: Tell your healthcare professional if symptoms are persistent or severe. (1) (2)
Allergic reaction (mild)
What to notice: Specific symptom detail was not established in the sources reviewed for this article; the sources support that a few allergic reactions have been reported.
What to do: Seek medical assessment; the clinician will advise whether the supplement can be continued. (2)
Severe allergic or anaphylactic reaction
What to notice: Specific symptom detail was not established in the sources reviewed for this article; the sources support that anaphylactic reactions are possible in people with a history of salicylate allergy.
What to do: Seek emergency medical attention immediately if you suspect a severe allergic reaction. Let the clinician you see advise on whether willow bark can be continued. (1)
Unusual bleeding or bruising
What to notice: Specific symptom detail was not established in the sources reviewed for this article; the sources support a general increased bleeding risk, particularly with anticoagulant or antiplatelet medicines.
What to do: Contact your healthcare professional promptly. Do not make any change to prescription blood-thinning medicines yourself; let the clinician you see advise on whether to continue or stop willow bark. (2)
Heavy-metal contamination concern (source-dependent)
What to notice: Clinical toxicity manifestations from willow-bark heavy-metal contamination were not established in the sources reviewed for this article. The sources describe a source-dependent contamination risk (e.g., cadmium) rather than an established toxicity profile.
What to do: Heavy-metal contamination is a recognised source-dependent safety concern for willow bark. Product-testing and consumer-verification guidance were not established in the sources reviewed for this article; discuss any concerns with a healthcare professional. (1)
Serious warnings
Anaphylaxis — emergency
Symptoms: Specific symptom detail was not established in the sources reviewed for this article; the sources support that anaphylactic reactions are possible in people with a history of salicylate allergy.
Action: Seek emergency medical attention immediately if you suspect a severe allergic reaction. Let the clinician you see advise on whether willow bark can be continued. (1)
Reye syndrome risk in children — important
Symptoms: Specific symptom detail was not established in the sources reviewed for this article; Reye syndrome is a recognised class-level concern for salicylate-containing products used in children during viral illness.
Action: Willow bark is not recommended for children or adolescents, especially during or after viral illness; discuss with a healthcare professional. Specific Reye-syndrome symptom guidance was not established in the sources reviewed for this article — seek prompt medical attention for any symptoms of concern in a child during or after a viral illness. (2)
Bleeding risk — important
Symptoms: Specific symptom detail was not established in the sources reviewed for this article; the sources support a general increased bleeding risk, particularly with anticoagulant or antiplatelet medicines.
Action: Seek medical attention promptly for any symptoms of concern, especially if you take anticoagulant or antiplatelet medicines. Let the clinician you see advise on whether to continue or stop willow bark. (2)
Heavy‑metal contamination — important
Symptoms: Symptom timing and toxicity manifestations were not established in the sources reviewed for this article. The sources describe willows as having a notable capacity to concentrate cadmium and other toxic metals from soil, which is a source-dependent contamination concern; testing and monitoring guidance are unresolved.
Action: Discuss any concerns about product purity with a healthcare professional. Specific testing or monitoring guidance was not established in the sources reviewed for this article. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Anticoagulant and antiplatelet drugs | Willow bark has a mild antiplatelet effect that may add to the blood‑thinning action of these medicines, increasing the risk of bleeding. | Discuss any combination with anticoagulant or antiplatelet drugs with your prescriber before use; do not stop or adjust your prescribed anticoagulant yourself. (2) |
| Aspirin and other salicylate medicines (e.g., salsalate, choline magnesium trisalicylate) | Combined use may compound salicylate‑related effects and side effects, potentially leading to salicylate toxicity. | Discuss any combination with aspirin or other salicylate medicines with a healthcare professional before use. (2) |
Pregnancy, breastfeeding, kidney/liver function, age
Children and adolescents
Willow bark should not be used in children or adolescents because of the risk of Reye syndrome in the context of viral illness. No safe pediatric dose has been established. The USP recommends a cautionary label statement: “Not for use in children.” (1) (2)
Pregnancy and breastfeeding
Salicylates cross the placenta and are eliminated slowly in newborns. Willow bark is not recommended during pregnancy or breastfeeding. The USP recommends a cautionary label statement against use in these populations. (1) (2)
People with bleeding disorders
Because of its mild antiplatelet effect, willow bark may increase bruising and bleeding risk in people with bleeding disorders or who are otherwise vulnerable to bleeding. Discuss use with your specialist. (2)
Monitoring
Before starting
- Confirm that no contraindications are present.
- Obtain a full medication history, especially prescription anticoagulants, antiplatelet agents, aspirin, or other salicylates.
- Inquire about history of salicylate allergy, bleeding vulnerability, pregnancy, or breastfeeding.
- Product-purity verification guidance (e.g., heavy-metal testing) was not established in the sources reviewed for this article.
During treatment
- Monitor for gastrointestinal side effects and signs of allergic reaction.
- Watch for any unusual bleeding or bruising, particularly in individuals on blood‑thinning medicines.
- In the monograph dosing context reviewed (short-term lower-back-pain treatment), do not exceed a 4-week treatment duration unless advised by a healthcare professional; a universal duration limit for all uses was not established in the sources reviewed.
- Long-term safety data beyond 8 weeks and specific heavy-metal monitoring guidance were not established in the sources reviewed for this article.
Storage
Storage information was not established in the sources reviewed for this article. Follow the storage instructions on the product label.
Professional information
Clinician-facing context only. Use the most current regional herbal monograph or regulatory guidance when advising patients on willow bark. Commercial product dosing varies, and a source-dependent heavy-metal contamination concern is documented.
International monograph consensus (ESCOP, British Herbal Compendium, German Commission E, Health Canada, as reported in web‑search summary; direct monograph verification pending)
Indication: Lower back pain (short‑term)
Dose summary: Willow bark extract standardised to 15% salicin: 393–1,572 mg per day (delivering 120–240 mg salicin) for up to 4 weeks. Confirm the exact extract and standardisation used in the specific product.
Renal context: Not established in the reviewed sources. No renal‑impairment dose adjustment has been validated for willow bark. (2)
United States (USP cautionary recommendation)
Indication: Any use of willow bark as a dietary supplement
Dose summary: No specific daily dose is endorsed by the USP. The USP recommends a cautionary label statement: “Not for use in children, women who are pregnant or nursing, or by persons with known sensitivity to aspirin.” Product dosages on the US market have been found to vary widely.
Renal context: Not established. (1)
Hepatic guidance
No hepatic‑impairment data were identified in the reviewed sources.
Overdose note
Specific overdose thresholds and management detail for willow bark were not established in the sources reviewed for this article. Suspected overdose or accidental large ingestion should be treated as a potential medical emergency and referred for immediate medical assessment. (1) (2)
Frequently asked questions
Is willow bark the same as aspirin?
Not exactly. Willow bark contains salicin, a compound chemically related to aspirin's salicylate mechanism. It also contains other compounds (flavonoids, tannins) and has been described in the literature reviewed as having a broader mechanism of action. It is not established as a substitute for aspirin, including for cardiovascular protection, in the sources reviewed for this article. (1)
Can I give willow bark to my child for a fever?
No. Willow bark should not be used in children because of the risk of Reye syndrome, especially during viral illnesses. The USP explicitly cautions against use in children. (1) (2)
Is it safe to take willow bark with my blood-thinning medicine?
If you take anticoagulant or antiplatelet drugs , discuss willow bark with your doctor before use and only under their guidance. The supplement has a mild blood-thinning effect that may add to your medicine's action and increase your bleeding risk. Always tell your prescriber about any supplement you are considering. (2)
How do I know my willow bark supplement is free of heavy metals?
Willows can accumulate cadmium and other heavy metals from contaminated soil. Product-testing and consumer-verification guidance were not established in the sources reviewed for this article; discuss any concerns about a product's purity with your healthcare professional. (1)
What is the mechanism of action of willow bark?
Salicin is the primary active constituent of willow bark; the bark also contains flavonoids and tannins. The USP safety review describes willow bark as having a broader mechanism of action than aspirin alone and, per the literature it reviewed, characterises it as devoid of the serious adverse events associated with aspirin — this is a literature characterisation from the reviewed source, not an independently confirmed clinical safety guarantee, particularly for long-term use or at-risk populations. (1) (2)
References
- United States Pharmacopeia Safety Review of Willow BarkUnited States Pharmacopeia (published in PubMed Central) · United States · accessed 2026-08-05 · source 1
- Consensus dosing and safety from European and international herbal monographs and USP cautionary labeling (WebSearch summary)Multiple (ESCOP, British Herbal Compendium, German Commission E, Health Canada, European monograph, USP) · International · accessed 2026-08-05 · source 2
- FEMICLEAR GENITAL HERPES SYMPTOMS MULTISYMPTOM (LEMONGRASS, WILLOW BARK EXTRACT) OINTMENT [ORGANICARE NATURE'S SCIENCE, LLC] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- willow bark — RxNorm normalized drug concept (RXCUI 260012)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 4
Brand names by country
Single-ingredient willow bark names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Willow Bark (various dietary supplement brands)current monograph · varies; no standardised pharmaceutical strength – typical products are labelled with extract amount (e.g., 400 mg) and may be standardised to salicin content (commonly 15 %); daily intake per monograph guidance is equivalent to 120–240 mg salicin · Not a single approved product; available as a dietary supplement from multiple manufacturers – see individual product labels for responsible party
United Kingdom
- Willow Bark (herbal product, various brands)current monograph · typical daily dose per ESCOP/British Herbal Compendium consensus: extract equivalent to 120–240 mg salicin (e.g., 393–1 572 mg extract standardised to 15 % salicin) · No single marketing authorisation; available as a traditional herbal medicinal product or food supplement depending on product registration
Canada
- Willow Bark (Natural Health Product – monograph status unconfirmed)unverified monograph · WebSearch summary suggests Health Canada monograph may recommend 120–240 mg salicin/day; direct monograph not accessed – product‑specific strengths unknown · Health Canada Natural Health Product monograph could not be verified directly; placeholder – requires direct monograph review