Herbal Monograph
White willow
Salix alba L.
Salicaceae
Nature's original aspirin — cooling analgesic, anti-inflammatory, and antipyr...
Overview
Plant Description
Large deciduous tree, 10-30 m tall at maturity, with a trunk up to 1 m in diameter and an irregular, often-leaning crown of ascending to spreading branches. Bark grey-brown, becoming deeply fissured and ridged with age. Young twigs slender, yellowish-green to olive-brown, flexible, and finely pubescent. Leaves alternate, lanceolate to narrowly elliptical, 5-12 cm long, 1-2.5 cm wide, with finely serrate margins, acuminate apex, and cuneate base. Upper leaf surface dark green, lower surface characteristically silvery-white due to a dense covering of silky, appressed hairs — the feature for which the species is named ('alba' meaning white). Stipules small, lanceolate, caducous. Dioecious: male and female catkins borne on separate trees, appearing with or just before the leaves in spring. Male catkins cylindrical, 4-5 cm long, with yellow stamens. Female catkins similar length, green, maturing to produce small capsules containing numerous tiny seeds with cottony hairs for wind dispersal. Root system wide-spreading, shallow, and aggressively water-seeking. Fast-growing but relatively short-lived for a tree (80-100 years typical).
Habitat
Riparian species strongly associated with waterways, floodplains, and wetlands. Thrives in moist to wet soils along rivers, streams, lakes, and in low-lying meadows. Tolerates periodic flooding and waterlogged soils. Prefers full sun. Grows in a wide range of soil types but performs best in deep, fertile, alluvial soils with neutral to slightly alkaline pH. Tolerant of urban conditions, pollution, and moderate salinity. Hardiness zones 4-9.
Distribution
Native to Europe (from the British Isles east through central Europe to western Russia), western and central Asia (Turkey, Iran, Caucasus, Central Asian republics), and North Africa. Widely naturalized in eastern North America, temperate South America, southern Australia, and New Zealand following introduction for ornamental, timber, and medicinal purposes. One of the most widely distributed Salix species globally.
Parts Used
Bark (Salicis cortex)
Preferred: Dried bark for decoction; standardized dry extract (for clinical dosing standardized to salicin content); tincture
The dried bark of young branches and twigs is the official medicinal part, specified in the European Pharmacopoeia, EMA/HMPC monograph, Commission E, ESCOP, and BHP. The bark contains the therapeutically active phenolic glycosides (salicin, salicortin, tremulacin) as well as tannins, flavonoids, and other polyphenols. Bark from 2-3 year old coppiced or pollarded branches has the highest salicin concentration. The European Pharmacopoeia monograph for 'Salicis cortex' covers bark from S. alba and several other Salix species (S. purpurea, S. daphnoides, S. fragilis) and their hybrids, requiring minimum 1.5% total salicylic derivatives expressed as salicin.
Leaf
Preferred: Fresh or dried leaf infusion (folk use only)
Leaves have been used in some folk traditions but contain lower concentrations of salicin compared to bark. Not included in any major pharmacopeial monograph for therapeutic use. Leaf preparations are not recommended as a substitute for bark preparations in clinical practice.
Key Constituents
Phenolic glycosides (salicylates)
The phenolic glycoside fraction is the primary active constituent group responsible for the analgesic, anti-inflammatory, and antipyretic effects. However, metabolism of 240 mg salicin (the standard clinical dose) yields only approximately 113 mg salicylic acid — far below the 500-1000 mg dose of aspirin required for equivalent analgesic effect. This pharmacokinetic discrepancy indicates that the clinical effects of willow bark cannot be explained by salicin/salicylic acid alone, and that other constituents (polyphenols, flavonoids) contribute significantly to the overall therapeutic effect. The EMA assessment report and multiple pharmacological studies confirm this multi-component mechanism.
Tannins and polyphenols
The high tannin content (8-20%) contributes significantly to the anti-inflammatory and astringent actions of willow bark. Tannins precipitate proteins on mucosal surfaces, creating a protective layer that reduces inflammation and secretion. This astringent action on the GI mucosa may explain the clinical observation that willow bark is better tolerated gastrointestinally than synthetic aspirin. Polyphenols also contribute antioxidant effects and may inhibit NF-kB signaling independently of the salicylate pathway.
Flavonoids
The flavonoid fraction contributes meaningfully to the anti-inflammatory effect of whole willow bark extract. In vitro studies (Fiebich and Chrubasik, 2004) demonstrated that polyphenols and flavonoids in willow bark inhibit the release of inflammatory mediators (TNF-alpha, PGE2) through mechanisms distinct from the salicylate pathway. This synergistic, multi-component mechanism distinguishes willow bark from isolated salicin or synthetic aspirin.
Other constituents
Minor constituents contribute ancillary antioxidant and anti-inflammatory effects. The phenolic acid content adds to the total polyphenol load of the extract.
Herbal Actions
The most clinically documented action. Willow bark extract standardized to 240 mg salicin daily has demonstrated significant pain reduction in multiple RCTs for low back pain and osteoarthritis. The analgesic mechanism involves conversion of salicin to salicylic acid (COX inhibition) plus direct anti-inflammatory effects of the polyphenol fraction (NF-kB inhibition, TNF-alpha suppression). Commission E approved for 'diseases accompanied by fever, rheumatic ailments, headaches.' The analgesic effect is slower in onset but more sustained than aspirin, consistent with the prodrug nature of salicin and the multi-component mechanism.
[1, 2, 4, 9]Reduces inflammation
Demonstrated anti-inflammatory activity through multiple pathways: (1) salicylic acid-mediated COX inhibition (though lacking the irreversible acetylation of aspirin), (2) polyphenol-mediated inhibition of NF-kB transcription factor, (3) flavonoid-mediated reduction of TNF-alpha and PGE2 release, (4) tannin-mediated astringent protection of inflamed surfaces. This multi-target mechanism is broader than aspirin's primary COX-inhibition and may explain the clinical efficacy despite relatively low salicylate doses.
[1, 2, 5, 14, 15]Fever reduction is one of the oldest and most well-documented uses of willow bark, dating to Edward Stone's 1763 report to the Royal Society. Commission E approved for 'diseases accompanied by fever.' The antipyretic mechanism operates through salicylic acid-mediated inhibition of prostaglandin synthesis in the hypothalamic thermoregulatory center. EMA classifies the use for 'relief of fever associated with common cold' as a traditional use indication.
[1, 2, 4]Commission E specifically approved willow bark for 'rheumatic ailments.' The combination of analgesic and anti-inflammatory actions provides symptomatic relief in both osteoarthritis and inflammatory rheumatic conditions. Clinical trials have demonstrated efficacy in osteoarthritis (Schmid et al., 2001) and low back pain (Chrubasik et al., 2000). The EMA monograph classifies 'short-term treatment of low back pain' as a well-established use.
[1, 2, 9, 11]Tightens and tones tissue, reduces secretions
Due to the high tannin content (8-20%) of the bark. Tannins precipitate proteins on mucosal surfaces, reducing secretion and inflammation. This astringent action is relevant to traditional uses for diarrhea, dysentery, and wound healing. The Eclectics valued willow bark specifically for its astringent-tonic combination. Contributes to the GI-protective profile relative to aspirin.
[4, 7, 17]Classified as a bitter tonic in the Eclectic and British Herbal traditions. The bitter taste of the bark stimulates digestive secretions and appetite. Felter and Lloyd described willow bark as 'tonic, antiperiodic, and an astringent bitter.' The BHP lists it as a bitter tonic for use in convalescence and debility.
[7, 17]Prevents or slows oxidative damage to cells
The polyphenol and flavonoid content provides significant antioxidant capacity. Catechins, condensed tannins, and flavonoid glycosides scavenge free radicals and reduce oxidative stress. This action is synergistic with the anti-inflammatory effects and may contribute to tissue protection in chronic inflammatory conditions.
[15]Therapeutic Indications
Musculoskeletal System
Low back pain (acute exacerbation of chronic)
EMA well-established use indication: 'short-term treatment of low back pain.' Based on the Chrubasik et al. (2000) RCT of 210 patients, which demonstrated that willow bark extract standardized to 240 mg salicin daily was significantly superior to placebo for pain relief (39% of patients pain-free vs 6% placebo, P<0.001). A subsequent open comparative trial (Chrubasik et al., 2001) showed comparable efficacy to rofecoxib (Vioxx) 12.5 mg daily. Commission E also approved for 'rheumatic ailments.'
[1, 2, 9, 10]Osteoarthritis (knee and hip)
Schmid et al. (2001) RCT of 78 patients with hip or knee osteoarthritis found that willow bark extract (240 mg salicin/day) produced a 14% reduction in WOMAC pain score versus 2% with placebo after 2 weeks (P<0.05). The effect size was modest and the trial duration short. A Cochrane-style systematic review (Vlachojannis et al., 2009) and subsequent meta-analysis (Wider et al., 2023) found moderate evidence of efficacy for musculoskeletal pain. EMA classifies use for 'relief of minor articular pain' as a traditional use indication.
[2, 11, 13]Rheumatic conditions (general)
Commission E approved indication: 'rheumatic ailments.' Long-standing traditional use for joint and muscle pain of rheumatic origin across European, Eclectic, and folk traditions. The anti-inflammatory and analgesic actions provide pharmacological rationale. Biegert et al. (2004) RCT comparing willow bark to placebo in rheumatoid arthritis found no significant difference, suggesting efficacy may be limited to non-inflammatory or mildly inflammatory arthritides rather than active autoimmune joint disease.
[1, 4, 12]Nervous System
Headache
Commission E approved indication: 'headaches.' EMA traditional use indication: 'for relief of headache.' One of the oldest recorded uses of willow bark. The analgesic mechanism is relevant to tension-type and mild to moderate headaches. No controlled clinical trials have specifically evaluated willow bark for headache as a primary endpoint, but the approval is based on the well-documented analgesic pharmacology and long traditional use record.
[1, 2, 4]immune-fever
Fever associated with common cold and influenza
Commission E approved for 'diseases accompanied by fever.' EMA traditional use indication: 'for the relief of fever associated with common cold.' Antipyretic action is mediated by salicylic acid inhibition of prostaglandin synthesis in the hypothalamic thermoregulatory center. Historical basis dates to Edward Stone's 1763 clinical report on willow bark for intermittent fevers. Hoffmann recommends willow bark as a cooling febrifuge.
[1, 2, 4]gastrointestinal
Diarrhea and dysentery (chronic, with debility)
Eclectic and traditional use based on the astringent-tonic properties of the bark. The high tannin content (8-20%) provides astringent activity on the intestinal mucosa. Felter and Lloyd (King's American Dispensatory): 'In chronic diarrhea and dysentery, the tonic and astringent combination of the willow renders it very eligible.' Not a primary modern indication — included for completeness of the traditional record.
[7, 17]Dyspepsia with digestive debility
Eclectic use as a bitter tonic for 'dyspepsia connected with debility of the digestive organs' (Felter and Lloyd). The bitter taste of salicin glycosides stimulates digestive secretion. Historical rather than modern indication.
[17]Energetics
Temperature
cool
Moisture
dry
Taste
Tissue States
hot/excitation, damp/stagnation, lax/atony
Willow bark is cooling and drying in Western energetic assessment. Its pronounced bitterness reflects the salicylate glycoside and polyphenol content, while the strong astringency derives from the high tannin content (8-20%). Energetically indicated for hot, inflammatory conditions with tissue laxity — e.g., inflamed joints with swelling, febrile states, hot headaches. The cooling, drying nature makes it less suited for cold, deficient, dry constitutions. Hoffmann classifies it among the cooling anti-inflammatory herbs appropriate for acute hot inflammatory states. The bitter-astringent combination was recognized by the Eclectics as particularly useful for convalescence with digestive weakness and loose stools.
Traditional Uses
European traditional herbalism / Western Herbalism
- Fever reduction and management of febrile illness
- Relief of headache and general pain
- Anti-inflammatory for joint and muscle pain
- Rheumatic conditions and gout
- Bitter tonic for convalescence
"Hoffmann (2003): 'Willow bark is a traditional remedy with a long history of use in Europe for conditions associated with pain, inflammation, and fever. It is the original source of salicylic acid, the precursor to aspirin. The bark is used for the treatment of rheumatic and arthritic conditions, for the management of fever in colds and influenza, and for headache and general pain. Its astringent tannins contribute an additional tonic and GI-protective effect that distinguishes it from synthetic aspirin.'"
[4]
German phytotherapy (Commission E / ESCOP)
- Diseases accompanied by fever
- Rheumatic ailments
- Headaches
"Commission E approved willow bark for 'diseases accompanied by fever, rheumatic ailments, headaches.' The ESCOP monograph expanded the indication set to include 'low back pain, osteoarthritic and rheumatic pain, fever associated with common cold.' ESCOP specifies standardized preparations delivering 120-240 mg salicin per day."
Eclectic medicine (American)
- Tonic and antiperiodic (intermittent fevers)
- Astringent bitter for dyspepsia and digestive debility
- Chronic diarrhea and dysentery
- Passive hemorrhages and chronic mucous discharges
- Convalescence from acute diseases
- Worms (anthelmintic)
"Felter and Lloyd (King's American Dispensatory, 1898): 'Willow bark is tonic, antiperiodic, and an astringent bitter. It has been given in intermittents, dyspepsia connected with debility of the digestive organs, passive hemorrhages, chronic mucous discharges, in convalescence from acute diseases, and in worms. In chronic diarrhea and dysentery, the tonic and astringent combination of the willow renders it very eligible.'"
[17]
Classical antiquity
- Pain relief and inflammation
- Treatment of ear pain
- Gout and joint conditions
- Fever reduction
"Dioscorides (De Materia Medica, c. 70 CE) recommended willow bark and leaf decoctions for gout, ear pain, and as a contraceptive. The attribution to Hippocrates (c. 400 BCE) of prescribing willow leaf tea for pain during childbirth is frequently cited but has been questioned by historians who note that direct references in the Hippocratic corpus are ambiguous. Edward Stone's 1763 letter to the Royal Society is the earliest well-documented clinical report: he described treating approximately 50 patients suffering from intermittent fever (ague) with powdered white willow bark, noting dramatic antipyretic effects."
[19]
English herbalism (Culpeper)
- Staunching wounds and bleeding
- Treatment of corns and foot complaints
- Diuretic (to 'provoke urine')
"Culpeper (The Complete Herbal, 1653) described multiple uses for willow: 'The leaves bruised and boiled in wine, and drunk, stays the heat of lust in man or woman... The decoction of the leaves or bark in wine... is good to stay vomiting... The burnt ashes of the bark, being mixed with vinegar, takes away warts, corns, and other risings in the feet and toes.' Notably, Culpeper did not specifically describe analgesic properties, though he valued willow for its cooling astringent qualities."
[18]
Modern Research
Low back pain
Randomized double-blind trial of willow bark extract for acute exacerbation of chronic low back pain.
Findings: Chrubasik et al. (2000) randomized 210 patients with exacerbation of chronic low back pain to receive willow bark extract delivering 120 mg salicin/day, 240 mg salicin/day, or placebo for 4 weeks. The primary endpoint was the proportion of patients pain-free (visual analog scale score less than or equal to 2 on 5 consecutive days) without rescue medication (tramadol) in the final week. Results: 39% of the high-dose (240 mg) group, 21% of the low-dose (120 mg) group, and 6% of the placebo group were pain-free (P<0.001 for high dose vs placebo). A significant dose-response relationship was demonstrated.
Limitations: Relatively short duration (4 weeks). Patients in clinical trials were selected for exacerbations of chronic pain, limiting generalizability to acute or subacute presentations. The 120 mg dose showed only modest superiority over placebo.
[9]
Comparison with rofecoxib (Vioxx) for low back pain
Open randomized controlled study comparing willow bark extract to rofecoxib for chronic low back pain.
Findings: Chrubasik et al. (2001) randomized 228 patients with chronic low back pain to willow bark extract (240 mg salicin/day) or rofecoxib 12.5 mg/day for 4 weeks in an open-label design. Both treatments produced similar pain relief (WOMAC-validated visual analog scale). The authors concluded that willow bark extract was non-inferior to rofecoxib for low back pain, with potentially lower costs.
Limitations: Open-label (not blinded), limiting reliability. Rofecoxib was subsequently withdrawn from the market due to cardiovascular safety concerns, making the comparator clinically obsolete. No placebo arm in this trial.
[10]
Osteoarthritis
Randomized placebo-controlled double-blind trial of standardized willow bark extract in patients with hip or knee osteoarthritis.
Findings: Schmid et al. (2001) randomized 78 patients with osteoarthritis of the hip or knee to willow bark extract (240 mg salicin/day) or placebo for 2 weeks. The WOMAC pain dimension showed a statistically significant 14% reduction in the willow bark group versus 2% in the placebo group (P<0.05). However, the absolute effect size was modest.
Limitations: Small sample size (n=78). Very short duration (2 weeks), insufficient to assess sustained benefit. The modest absolute effect size raises questions about clinical significance despite statistical significance. A larger, longer trial is needed.
[11]
Mechanism of action — distinct from aspirin
Investigation of the anti-inflammatory mechanism of willow bark extract compared to aspirin, examining polyphenol contributions.
Findings: Fiebich and Chrubasik (2004) demonstrated in vitro that an ethanolic willow bark extract inhibited the release of PGE2, COX-2 expression, and TNF-alpha in LPS-stimulated human monocytes. Crucially, the anti-inflammatory effect could not be fully attributed to the salicin content alone — the polyphenol and flavonoid fraction contributed significantly. Salicin lacks the acetyl group of aspirin and therefore does not irreversibly inhibit COX enzymes by acetylation. Multiple studies have confirmed that the mechanism of willow bark is broader and more complex than that of aspirin, involving NF-kB inhibition, TNF-alpha suppression, and antioxidant activity from the polyphenol fraction.
Limitations: In vitro study; dose extrapolation to clinical use is indirect. The relative contributions of individual compounds to the overall clinical effect remain incompletely characterized.
Systematic review of willow bark for musculoskeletal pain
Systematic review evaluating the effectiveness of willow bark for musculoskeletal pain conditions.
Findings: Vlachojannis et al. (2009) systematically reviewed the clinical evidence for willow bark in musculoskeletal pain. They identified two high-quality RCTs (Chrubasik 2000, Schmid 2001) and several open or comparative trials. The review concluded there is moderate evidence that willow bark extract delivering 240 mg salicin daily is effective for short-term treatment of low back pain, and limited evidence for osteoarthritis. The authors noted that the evidence base remained small and further high-quality trials were needed.
Limitations: Limited number of adequately powered RCTs available for review. Heterogeneity of outcome measures across trials limited meta-analysis. Most trials were conducted by the same research group (Chrubasik), raising concerns about independent replication.
[13]
USP safety review
Comprehensive safety review of willow bark conducted by the United States Pharmacopeia.
Findings: Oketch-Rabah et al. (2019) conducted a comprehensive safety review for the USP. They found no serious adverse events in clinical trials of willow bark extracts delivering 120-240 mg salicin daily for up to 8 weeks. Gastrointestinal adverse effects were the most commonly reported but were mild and infrequent. Willow bark did not significantly affect platelet aggregation at standard doses — unlike aspirin. However, the review noted that metabolism of 240 mg salicin could yield approximately 113 mg salicylic acid, comparable to the salicylic acid yield of low-dose aspirin (81 mg ASA yields ~62 mg salicylic acid). The USP recommended cautionary labeling: 'Not for use in children, women who are pregnant or nursing, or by persons with known sensitivity to aspirin.'
Limitations: The review relied on a limited number of clinical trials with relatively short durations. Long-term safety data are lacking. The theoretical risk of Reye syndrome in children is extrapolated from aspirin data and has not been documented with willow bark specifically.
[16]
Preparations & Dosage
Decoction
Strength: 2-3 g dried bark per 250 mL water
Place 2-3 g of finely chopped or coarsely powdered dried willow bark in 250 mL of cold water. Bring to a boil and simmer gently for 10-15 minutes. Strain while hot. The decoction is necessary (rather than a simple infusion) because the hard, woody bark requires prolonged heat to release the salicylate glycosides and tannins effectively.
2-3 g dried bark per cup as decoction, 3-4 times daily; or equivalent to 120-240 mg total salicin per day
3-4 times daily
For low back pain: up to 4 weeks (EMA recommendation). For fever: short-term use during acute febrile illness only. For articular pain: up to 4 weeks, then reassess.
Not recommended for children under 18 years due to theoretical risk of Reye syndrome (salicylate content)
Decoction is the traditional preparation method and extracts both the salicylate glycosides and the tannin/polyphenol fraction. The resulting liquid is strongly bitter and astringent. Can be sweetened with honey if desired. The aqueous decoction delivers a broader constituent profile than standardized salicin-only extracts, including tannins, polyphenols, and flavonoids.
Tincture
Strength: 1:5 dried bark in 25-45% ethanol
Macerate dried willow bark in 25-45% ethanol at a ratio of 1:5 for 2-4 weeks with regular agitation. Press and filter. The relatively low alcohol percentage (compared to many tinctures) is appropriate because the key constituents (salicin, tannins) are water-soluble or soluble in hydroalcoholic mixtures.
5-8 mL of 1:5 tincture (in 25% ethanol), 3 times daily (BHP dosage). Alternative: 2-4 mL of 1:5 tincture (in 45% ethanol), 2-3 times daily.
3 times daily
Up to 4 weeks, then reassess
Not recommended for children under 18 years
Tincture offers convenience and longer shelf life compared to decoction. The hydroalcoholic menstruum extracts a full spectrum of constituents including salicylate glycosides, tannins, and flavonoids. Can be added to water or juice to mitigate the bitter taste.
standardized extract
Strength: Standardized to salicin content; typically 15-25% salicin in dry extract
Commercially available dry extracts standardized to salicin content. Most clinical trials used a proprietary extract (Assalix/STW 33-I) standardized to deliver 120-240 mg total salicin per day, typically in divided doses.
Equivalent to 120-240 mg salicin per day in divided doses. For low back pain, 240 mg salicin/day was the effective dose in the Chrubasik (2000) RCT. ESCOP recommends preparations corresponding to 120-240 mg total salicin for musculoskeletal pain.
Usually divided into 2-3 doses per day
Up to 4 weeks for musculoskeletal pain (EMA). Short-term for fever.
Not recommended for children under 18 years
Standardized dry extracts are the form used in all major clinical trials and are the basis for the EMA well-established use designation. Standardization to salicin ensures consistent dosing but does not capture the full polyphenol/flavonoid profile, which contributes to the therapeutic effect. Some products are standardized to total salicylic derivatives (including salicortin) rather than salicin alone.
fluid extract
Strength: 1:1 dried bark in 25% ethanol
Liquid extract prepared at 1:1 concentration in 25% ethanol. More concentrated than a standard tincture.
1-3 mL, 3 times daily
3 times daily
Up to 4 weeks
Not recommended for children under 18 years
Fluid extract is the most concentrated liquid preparation. BHP specifies this as one of the official preparations. Due to higher concentration, smaller volumes are needed compared to tincture.
[7]
Safety & Interactions
Class 2d
Other specific use restrictions apply (AHPA Botanical Safety Handbook)
Contraindications
Cross-reactivity between willow bark salicylates and aspirin allergy is documented. Individuals with aspirin-sensitive asthma, urticaria, or anaphylaxis should not use willow bark preparations. The USP safety review recommends the cautionary statement: 'Not for use by persons with known sensitivity to aspirin.' Although the salicylate profile of willow bark differs from aspirin (no acetyl group), the metabolite salicylic acid is common to both, and cross-reactive hypersensitivity cannot be ruled out.
Due to the theoretical risk of Reye syndrome, a rare but potentially fatal hepatic encephalopathy associated with salicylate use in children with viral infections. While Reye syndrome has been documented specifically with aspirin (not willow bark), the salicylate content of willow bark creates a theoretical risk that cannot be ethically tested. All major regulatory bodies (EMA, USP, AHPA) recommend against use in children. The EMA monograph explicitly states willow bark preparations 'should not be used in children and adolescents under 18 years of age.'
Although willow bark is generally better tolerated gastrointestinally than aspirin (due to the gastroprotective tannin content and the absence of direct COX-1 inhibition by the prodrug salicin), it should not be used in patients with active peptic ulcers or GI bleeding due to the salicylate content.
Drug Interactions
| Drug / Class | Severity | Mechanism |
|---|---|---|
| Anticoagulants (warfarin, heparin, enoxaparin) (Anticoagulants) | theoretical | Salicylic acid (the active metabolite of salicin) can displace warfarin from plasma protein binding sites, potentially increasing free warfarin levels. Additionally, salicylates can impair platelet function, though the USP review found that willow bark at standard doses did not significantly affect platelet aggregation in clinical studies. The interaction is classified as theoretical because clinical case reports documenting the interaction are lacking, but the pharmacological basis is plausible. |
| NSAIDs (ibuprofen, naproxen, diclofenac, etc.) (Non-steroidal anti-inflammatory drugs) | theoretical | Additive salicylate load and additive risk of gastrointestinal mucosal damage. Concurrent use of willow bark with NSAIDs increases the total salicylate/anti-inflammatory burden and may increase GI adverse effects. |
| Antiplatelet agents (aspirin, clopidogrel, ticlopidine) (Antiplatelet agents) | theoretical | Potential additive inhibition of platelet function due to salicylate content. The risk is lower than with aspirin because salicin-derived salicylic acid does not irreversibly acetylate COX-1, but caution is warranted. |
| Methotrexate (Antimetabolite / DMARD) | theoretical | Salicylates can reduce renal clearance of methotrexate and displace it from plasma protein binding, potentially increasing methotrexate toxicity. This is a well-established interaction class with aspirin; the relevance to willow bark is extrapolated from the salicylate content. |
| Phenytoin, valproic acid (Anticonvulsants) | theoretical | Salicylates can displace phenytoin and valproic acid from plasma protein binding sites, potentially increasing free drug levels and toxicity risk. |
Pregnancy & Lactation
Pregnancy
unsafe
Lactation
unsafe
Salicylates cross the placenta and are excreted in breast milk. The USP safety review recommends: 'Not for use in women who are pregnant or nursing.' The EMA monograph states that willow bark preparations 'should not be used during pregnancy and lactation' due to insufficient safety data and the known risks of salicylates in pregnancy (potential for bleeding complications, premature closure of the ductus arteriosus in late pregnancy). AHPA classifies Salix alba as Class 2d, indicating 'specific use restrictions apply.' While the salicylate dose from standard willow bark use is lower than therapeutic aspirin doses, the precautionary principle applies given the availability of safer alternatives for pain and fever during pregnancy.
Adverse Effects
References
Monograph Sources
- [1] Blumenthal, M., Busse, W.R., Goldberg, A., et al.. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council / Integrative Medicine Communications (1998) . ISBN: 978-0965555500
- [2] Committee on Herbal Medicinal Products (HMPC). European Union herbal monograph on Salix [various species including S. purpurea L., S. daphnoides Vill., S. fragilis L.], cortex. European Medicines Agency (2017)
- [3] ESCOP (European Scientific Cooperative on Phytotherapy). ESCOP Monographs: The Scientific Foundation for Herbal Medicinal Products — Salicis cortex (Willow Bark). ESCOP / Thieme (2009) . ISBN: 978-1901964264
- [4] Hoffmann, D.. Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press (2003) . ISBN: 978-0892817498
- [5] Mills, S., Bone, K.. Principles and Practice of Phytotherapy: Modern Herbal Medicine (2nd edition). Churchill Livingstone / Elsevier (2013) . ISBN: 978-0443069925
- [6] Gardner, Z., McGuffin, M. (eds.). American Herbal Products Association's Botanical Safety Handbook (2nd edition). CRC Press (2013) . ISBN: 978-1466516946
- [7] British Herbal Medicine Association. British Herbal Pharmacopoeia. BHMA (1983)
- [8] Brinker, F.. Herbal Contraindications and Drug Interactions (4th edition). Eclectic Medical Publications (2010) . ISBN: 978-1888483147
Clinical Studies
- [9] Chrubasik, S., Eisenberg, E., Balan, E., et al.. Treatment of low back pain exacerbations with willow bark extract: a randomized double-blind study. American Journal of Medicine (2000) ; 109 : 9-14 . DOI: 10.1016/S0002-9343(00)00442-3 . PMID: 10936472
- [10] Chrubasik, S., Kunzel, O., Model, A., et al.. Treatment of low back pain with a herbal or synthetic anti-rheumatic: a randomized controlled study. Willow bark extract for low back pain. Rheumatology (2001) ; 40 : 1388-1393 . DOI: 10.1093/rheumatology/40.12.1388 . PMID: 11752510
- [11] Schmid, B., Ludtke, R., Selbmann, H.K., et al.. Efficacy and tolerability of a standardized willow bark extract in patients with osteoarthritis: randomized placebo-controlled, double blind clinical trial. Phytotherapy Research (2001) ; 15 : 344-350 . DOI: 10.1002/ptr.981 . PMID: 11406860
- [12] Biegert, C., Wagner, I., Ludtke, R., et al.. Efficacy and safety of willow bark extract in the treatment of osteoarthritis and rheumatoid arthritis: results of 2 randomized double-blind controlled trials. Journal of Rheumatology (2004) ; 31 : 2121-2130 . PMID: 15517622
- [13] Vlachojannis, J.E., Cameron, M., Chrubasik, S.. A systematic review on the effectiveness of willow bark for musculoskeletal pain. Phytotherapy Research (2009) ; 23 : 897-900 . DOI: 10.1002/ptr.2729 . PMID: 19140170
- [14] Fiebich, B.L., Chrubasik, S.. Effects of an ethanolic salix extract on the release of selected inflammatory mediators in vitro. Phytomedicine (2004) ; 11 : 135-138 . DOI: 10.1078/0944-7113-00338 . PMID: 15070163
- [15] Shara, M., Stohs, S.J.. Efficacy and Safety of White Willow Bark (Salix alba) Extracts. Phytotherapy Research (2015) ; 29 : 1112-1116 . DOI: 10.1002/ptr.5377 . PMID: 25997859
- [16] Oketch-Rabah, H.A., Marles, R.J., Brinckmann, J.A., et al.. United States Pharmacopeia Safety Review of Willow Bark. Planta Medica (2019) ; 85 : 1192-1202 . DOI: 10.1055/a-1007-5206 . PMID: 31604354
Traditional Texts
- [17] Felter, H.W., Lloyd, J.U.. King's American Dispensatory (18th edition, 3rd revision). Ohio Valley Company (1898)
- [18] Culpeper, N.. The Complete Herbal. Originally published 1653; numerous reprints (1653)
- [19] Mahdi, J.G., Mahdi, A.J., Mahdi, A.J., et al.. The historical analysis of aspirin discovery, its relation to the willow tree and antiproliferative and anticancer potential. Cell Proliferation (2006) ; 39 : 147-155 . DOI: 10.1111/j.1365-2184.2006.00377.x
Pharmacopeias & Reviews
- [20] European Pharmacopoeia Commission. European Pharmacopoeia — Salicis cortex (Willow Bark). Council of Europe / EDQM (2023)
Last updated: 2026-03-02 | Status: review
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