Black willow

Other Names

Crack willowDudley willowGoodding willowGulf black willowSalix ambigua PurshSalix denudata RafinesqueSalix dubia TrautvetterSalix falcata PurshSalix flavovirens HornemannSalix ligustrina F. MichauxSalix ludoviciana RafinesqueSalix nigraSalix nigra MarshallSalix nigra var. altissima SargentSalix nigra var. amygdaloides AnderssonSalix nigra var. brevifolia AnderssonSalix nigra var. brevijulis AnderssonSalix nigra var. falcata (Pursh) TorreySalix nigra var. lindheimeri C.K. SchneiderSalix nigra var. longifoliaSalix nigra var. marginataSalix nigra var. nigraSalix nigra var. vallicola DudleySalix nigra var. venulosa (Andersson) BebbSalix nigra var. wardiiSalix purshiana SprengelSauzScythe-leaved willowSouthwest black willowSouthwestern black willowSwamp willowWillow

Synopsis

Black Willow (Salix nigra): A Comprehensive Reference

1. Identity and Botanical Classification

Scientific Name and Taxonomy

Black willow is formally known as Salix nigra Marshall — a name first described by Humphry Marshall, known as the "Father of American Dendrology," in 1785. The scientific epithet derives from the Latin salix (willow) and nigra (black), referencing the tree's distinctively dark bark. Black willow belongs to the family Salicaceae, the willow family.

Other common names include "swamp willow," "Goodding willow," "southwestern black willow," "Dudley willow," and "sauz" (a Spanish-language name). In commerce and cosmetics, the species is often identified by its INCI designation Salix nigra (Willow) Bark Extract.

Botanical Description and Natural Habitat

Black willow is the largest willow with the most extensive range in North America. It is a medium to large, fast-growing, deciduous tree that typically grows to 30–60 feet tall on single or multiple trunks, topped by a spreading, rounded but sometimes irregular crown. It is the largest and most important New World willow, and in the lower Mississippi Valley attains commercial timber size, reaching 100–140 feet in height and up to 4 feet in diameter.

The bark of black willow is dark brown to black, developing deep grooves and a rough texture with shaggy scales as it ages. Narrow, lanceolate, finely toothed, medium to dark green leaves (to 6 inches long) taper to elongate tips. The species is dioecious, meaning it has separate male and female trees.

The tree is native to a large portion of North America, from New Brunswick and southern Ontario west to California and Arizona, and south to northern Florida and Texas; it is also found in parts of Mexico. It is native to moist to wet soils of floodplains, stream and river banks, swamps, marshes, sloughs, and ponds.

Parts Used and Common Preparations

Black willow differs from the more commercially ubiquitous white willow (Salix alba) in which plant part is considered most medicinally relevant. According to older botanical authors, particularly Michaux, the medicinal part is the bark of the root, though the bark of the trunk has also been employed; however, Eclectic physicians demonstrated that the bark of Salix nigra was of little value compared with preparations of the fresh aments (flowering catkins).

The aments (catkins) are the preferred preparation specifically associated with black willow, which is very different from white willow, where bark is the main ingredient. Preparations documented in historical and traditional literature include:

Fluid extract of the aments (buds/catkins) — the primary Eclectic preparation, made from fresh or dried flowering catkins
Bark decoctions — boiled preparations of root or stem bark used by various Native American tribes
Bark extract — standardized modern preparations, often reporting salicin content, used in dietary supplements and cosmetics
Topical applications — Salix nigra bark extract is used in skin-care formulations (INCI: Salix nigra Bark Extract)

2. Traditional and Historical Use

Native American Traditions

Black willow has been used by Native American communities for centuries as a medicinal remedy. Ethnobotanical uses by various Native American tribes include basketry and treatment of fever, headache, and coughs. The bark has been employed for centuries as an analgesic, and some Native American communities, such as the Cherokee, relied on it as a folk remedy for headaches and muscle tension. It has also been used as a fever reducer in traditional medicine.

Black willow roots, which are very bitter, have been used as a substitute for quinine in the past. The USDA Plant Guide documents that aboriginal peoples of North America used various plant parts of black willow for uses including drugs, with applications recorded among tribes such as the Koasati.

Eclectic Medicine (19th–Early 20th Century)

The Eclectic School of medicine, which emerged in the United States in the 1830s, arose from earlier botanical medicine movements and Native American herbal traditions; its practitioners primarily used plant-based drugs indigenous to the United States and developed a distinct "American materia medica." Black willow held a notable and distinctive place in this tradition.

Although it is not much used by herbalists today, black willow was used by the Eclectic physicians. The Eclectic Dispensatory described the plant's buds as having strong influence over sexual function. According to various Eclectic practitioners, the green aments or floral buds were considered a very active sexual depressant, useful in spermatorrhea, in all forms of sexual excitement, and in the nervous disturbances of the menstrual period.

The Eclectic literature, as preserved in King's American Dispensatory, also recorded the use of black willow for conditions such as spermatorrhea in its varied forms, prostatitis, cystitis, and ovaritis. Eclectic writers classified the aments as a "sexual sedative, slightly laxative," with a "sedative influence over undue sexual excitement, if caused by local irritation," used to relieve spermatorrhea, nymphomania, and sexual hyperesthesia. It was also considered useful in ovarian congestion and irritation, some forms of hysteria, cystitis, ovaritis, prostatitis, and nocturnal emissions.

A 19th-century medical report archived in PubMed Central, titled "On the Use of Salix Nigra (Aments)," documents an early clinical observation: a physician recorded finding a remedy in the fluid extract of Salix nigra aments (buds) from the common willow tree of Southern rivers, creeks, and lakes.

The historically documented dose in the Eclectic tradition was 20 to 30 minims (approximately 1.3–1.8 milliliters) of the fluid extract given four times a day.

Use as an Analgesic and Antipyretic Across Cultures

Willow and other salicylate-containing herbs have been used as analgesics for at least 2,000 years, recommended by physicians such as Paracelsus and Hippocrates. Although anecdotal accounts of willow bark extract as an anti-inflammatory drug have occurred since written records began — for example, by Hippocrates — the first convincing demonstration of a potent antipyretic effect of willow bark containing salicylates was made by the English clergyman Edward Stone in the late 18th century. In 1763, Stone wrote to the President of the Royal Society with "An account of the success of the bark of the willow in the cure of agues."

Native Americans used numerous willow species for their analgesic, anthelmintic, and hemostatic properties. The Cherokee, Iroquois, Inuit, and other tribes in the southwest all have documented historical ethnobotanical uses of willow species.

The aments, like the bark, were traditionally cited as being beneficial for gangrene; however, their main use in Eclectic medicine was as an anaphrodisiac.

3. Key Constituents and Active Compounds

Primary Phytochemicals

Salix nigra is a Salicaceae tree containing flavonoids, lignin, and phenolic compounds in its leaves; it has been used for its antiperiodic, antipyretic, sterile, antirheumatic, and pain-relieving effects. The genus Salix as a whole is exceptionally chemically diverse: it is traditionally used in folk medicine and represents a valuable source of biologically active compounds, among them salicin (a prodrug for salicylic acid); altogether, 322 secondary metabolites have been characterized in the genus, including flavonoids (flavonols, flavones, flavanones, isoflavones, flavan-3-ols, chalcones, dihydrochalcone, anthocyanins, and dihydroflavonols), phenolic glycosides, organic acids, non-phenolic glycosides, sterols and terpenes, simple phenolics, and lignans, in addition to volatiles and fatty acids.

Key constituents identified in willow bark by HPLC analysis include:

Salicin — a β-glucoside that converts to salicylic acid in the body, offering analgesic and antipyretic effects akin to aspirin. Along with salicin, phenolic acids — gallic, chlorogenic, p-hydroxybenzoic, syringic, p-coumaric, and trans-cinnamic acids — and flavonoids including epicatechin, rutin, quercetin, and naringenin have been identified and quantified by HPLC-DAD.
Additional phenolic glycosides — at least 13 different main compounds have been identified in willow bark, including saligenin, salicylic acid, salicin, isosalicin, picein, salidroside, triandrin, salicoylsalicin, salicortin, isosalipurposide, salipurposide, naringenin-7-O-glucoside, and tremulacin.
Tannins — condensed tannins provide astringent properties, which may aid in gut lining protection.
Flavonoids — quercetin and luteolin derivatives help scavenge free radicals, moderating oxidative stress.
Alkaloids, resins, and phenols — several phytochemicals including alkaloids, resins, and phenols have been found in S. nigra ethanolic plant extract.
Malic acid, pyrogallol, and mandelic acid — based on HPLC analysis, these three compounds have been identified specifically in S. nigra extracts.

Salicin Content and Variability

The phytochemical fingerprint varies across willow species — S. alba, S. purpurea, and S. nigra all differ in salicin percentage and secondary metabolites. Salicin was the dominant component in 11 out of 12 samples in one phytochemical screening study (it was not detected in leaves of S. alba in that study); salicin concentration ranged from 2.7 to 21.50 mg/g across species and plant parts.

Willow bark is a natural product that contains variable amounts of salicin; each willow bark product or batch may contain different amounts of salicin, which can change its effects and side effects — in contrast to aspirin, each tablet of which is standardized to contain the same amount of drug.

4. Mechanisms of Action

Salicin and the Salicylate Pathway

Mechanistically, salicin undergoes hydrolysis in the small intestine, releasing saligenin that is subsequently oxidized to salicylic acid. This metabolite suppresses prostaglandin synthesis by blocking cyclooxygenase (COX-1 and COX-2). The major metabolites of salicin are gentisic acid, salicylic acid, and salicyluric acid, with salicylic acid being the major component in serum; after oral ingestion of willow bark, peak levels of salicylic acid are found in less than 2 hours.

The bitter active ingredient with antipyretic activity in willow bark was called salicin, which was first isolated in 1829 by Leroux; on hydrolysis, salicin produced glucose and salicylic alcohol, which was metabolized to salicylic acid. Sodium salicylate was first used for the treatment of rheumatic fever and as an antipyretic agent in 1875.

Beyond Salicin: The Multi-Component Action

A critical distinction between willow bark and aspirin is that salicin alone does not fully explain the clinical activity of the whole extract. The well-known anti-inflammatory and analgesic effects of willow bark extract have been attributed to the content of salicin; however, pharmacological studies have shown that salicin alone, despite being involved in its therapeutic action, cannot fully explain its clinical efficacy.

Willow species contain only a low quantity of the prodrug salicin, which is metabolized during absorption into various salicylate derivatives; if calculated as salicylic acid, the daily salicin dose is insufficient to produce analgesia, as salicylic acid concentrations following an analgesic dose of aspirin are an order of magnitude higher. Flavonoids and polyphenols contribute to the potent willow bark analgesic and anti-inflammatory effect, and the multi-component active principle of willow bark provides a broader mechanism of action than aspirin.

Various in vitro and animal studies have demonstrated that the anti-inflammatory activity of willow bark extracts is associated with down-regulation of tumour necrosis factor α (TNF-α) and nuclear factor kB (NF-kB). Both flavonoids and polyphenols in willow bark have been shown to be attributed to anti-inflammatory effects.

Unlike the case of synthetic pharmaceuticals based on the activity of single chemical compounds, numerous phytochemical compounds in willow bark act in a beneficial manner by additive or synergistic activity at one or numerous target sites connected to physiological processes.

In contrast to synthetic aspirin, willow bark does not damage the gastrointestinal mucosa. In addition to the already well-known anti-inflammatory and analgesic effects, willow bark extract has been found to possess anti-proliferative and pro-apoptotic effects similar to NSAIDs; the different influence of willow bark on COX-1 and COX-2 mRNA expressions in comparison to NSAIDs might be relevant for prevention of undesirable side effects such as gastric erosions.

5. Scientific Evidence by Area of Use

5.1 Pain Relief and Musculoskeletal Conditions

Low Back Pain

The most clinically robust evidence for willow bark (including Salix nigra-containing preparations) comes from studies in low back pain. A key randomized double-blind trial (Chrubasik et al., 2000) enrolled 210 patients with an exacerbation of chronic low back pain who reported current pain of 5 or more out of 10 on a visual analog scale; they were randomly assigned to receive oral willow bark extract with either 120 mg (low dose) or 240 mg (high dose) of salicin, or placebo, with tramadol as the sole rescue medication, in a 4-week blinded trial; the principal outcome measure was the proportion of patients who were pain-free without tramadol for at least 5 days during the final week of the study.

The numbers of pain-free patients in the last week of treatment were 27 (39%) of 65 in the group receiving high-dose extract, 15 (21%) of 67 in the group receiving low-dose extract, and 4 (6%) of 59 in the placebo group (P <0.001); the response in the high-dose group was evident after only 1 week of treatment; significantly more patients in the placebo group required tramadol (P <0.001) during each week of the study; one patient suffered a severe allergic reaction, perhaps to the extract. This trial represents one of the more positive and adequately powered results in the willow bark clinical literature.

Osteoarthritis

A 2001 randomized, placebo-controlled, double-blind clinical trial by Schmid et al. assessed the clinical efficacy of a chemically standardized willow bark extract in the treatment of osteoarthritis; willow bark extract, in a dose corresponding to 240 mg salicin/day, was compared with placebo over 2 weeks; primary outcome was the pain dimension of the WOMAC Osteoarthritis Index, with secondary measures including stiffness and physical function dimensions and visual analogue scales; 78 patients participated (39 willow bark extract, 39 placebo). A statistically significant difference between the active treatment and the placebo group was observed in the WOMAC pain dimension (d = 6.5 mm, 95% CI 0.2–12.7 mm, p = 0.047); the WOMAC pain score was reduced by 14% from the baseline level after 2 weeks of active treatment, compared with an increase of 2% in the placebo group.

However, findings across trials have been mixed. A further 6-week randomized, controlled, double-blind trial (Biegert et al., 2004) studied 127 outpatients with hip or knee osteoarthritis with a WOMAC pain score of at least 30 mm; patients were randomized to receive willow bark extract corresponding to 240 mg of salicin/day, diclofenac 100 mg/day, or placebo. WOMAC pain scores decreased by 8 mm (17%) in the willow bark group and by 23 mm (47%) in the diclofenac group, compared with 5 mm (10%) in the placebo group; the difference between willow bark extract and placebo was not statistically significant. The osteoarthritis study suggested that the willow bark extract showed no relevant efficacy in patients with OA; similarly, the rheumatoid arthritis trial did not indicate efficacy of this extract in patients with RA.

Meta-Analysis on Arthritis

The first meta-analysis of RCTs to assess the clinical advantages of willow bark in diminishing pain and enhancing physical function in patients with arthritis (published in PMC) concluded that willow bark may be one of the alternative treatments for knee osteoarthritis. This meta-analysis included five studies with six RCTs consisting of 329 patients with arthritis; results showed significant differences in pain relief and improvement in physical status for patients with arthritis between willow bark treatment and placebo groups, and no significant differences in the risk of all adverse events between willow bark treatment and placebo. Owing to the potential bias, the certainty and evidence of the findings were still considered inadequate, and further RCTs were noted as needed to confirm results.

Evidence strength summary (pain/musculoskeletal): Despite its long history of use, only a few small clinical trials have been conducted that support the use of willow bark extracts in chronic low-back pain and osteoarthritis. Results are mixed across trials. The strongest positive data is for acute exacerbations of low back pain at higher doses (240 mg salicin/day); osteoarthritis results are inconsistent across studies.

5.2 Antimicrobial Activity

Scientists have studied the antibacterial activity of S. nigra leaf extract against various bacterial pathogens, including Escherichia coli, Salmonella typhi, and Salmonella paratyphi; S. nigra is known to possess antimicrobial activity, and several phytochemicals including alkaloids, resins, and phenols have been found in its ethanolic plant extract; it has shown antimicrobial activity against pathogenic microorganisms, especially Staphylococcus aureus.

Evidence strength (antimicrobial): All current evidence is in vitro (cell and culture experiments). No human clinical trials have been conducted on S. nigra specifically for antimicrobial applications.

5.3 Antiviral Activity

A study published in ACS Omega (2023) aimed to explore the antiviral activity of Salix nigra against the hepatitis C virus (HCV); the anti-HCV activity was established against stable Hep G2 cell lines expressing the HCV NS3 gene; various plant-derived compounds with anti-HCV activity were identified, making phytotherapy a promising alternative to conventional treatments. The study used two extraction methods (maceration and Soxhlet) and four solvents (n-hexane, methanol, ethyl acetate, and water) to obtain crude extracts; cytotoxicity testing showed that methanol (CC50 25 μg/mL) and water (CC50 30 μg/mL) extracts were highly toxic, while ethyl acetate and n-hexane (CC50 >200 μg/mL) extracts were less so.

Separately, a 2023 study published in Frontiers in Microbiology investigated the antiviral potential of willow (Salix spp.) bark hot water extracts against coronaviruses and enteroviruses: scientists showed that an extract of willow bark had a broad-spectrum antiviral effect in cell sample experiments. The authors also tested existing medical compounds derived from willow bark, as well as commercially prepared salixin extract and salixin powder; of these, only the salixin extract showed antiviral activity, suggesting that the success of the willow bark extract could result from the interactions of different bioactive compounds.

Evidence strength (antiviral): Entirely in vitro and preliminary. No human clinical trials exist for antiviral applications of S. nigra.

5.4 Anti-Proliferative and Apoptotic Effects

Acetylsalicylic acid (aspirin), like other NSAIDs, has been shown to exert anti-proliferative effects and to induce apoptosis in a variety of cell lines (e.g., colon, stomach, and prostate cancer cells); to investigate whether willow bark shares this property, a water extract (STW 33-1) and a polyphenol-rich fraction were tested using the colon-carcinoma cell line HT-29; both the extract and its polyphenol fraction showed significant anti-proliferative and pro-apoptotic effects on HT-29 cancer cells.

Evidence strength (anti-proliferative): In vitro data only. No human clinical trials on S. nigra or willow bark for cancer prevention or treatment have been conducted.

5.5 Antipyretic (Fever-Reducing) Activity

Studies on the genus Salix document analgesic, anti-inflammatory, antioxidant, anticancer, cytotoxic, antidiabetic, antimicrobial, antiobesity, neuroprotective, and hepatoprotective activities. Willow bark was used traditionally by herbalists for fever, headache, pain, and rheumatic complaints; in the late 19th century, the constituent salicylic acid was isolated from willow bark and went on to become the model for the development of aspirin (acetylsalicylic acid). However, direct clinical trials of S. nigra specifically as an antipyretic are lacking in the current literature.

5.6 Skin and Topical Applications

Willow bark extract, derived from several species of willow trees including black willow (Salix nigra), has been used for centuries in traditional medicine; the bark of these trees is rich in salicin, a compound that is metabolized into salicylic acid in the body when taken orally — often referred to as "nature's aspirin," and a widely used skin-care ingredient. The composition includes salicin, tannins, polyphenols, flavonoids, and phenolic acids, which collectively contribute to anti-inflammatory, antibacterial, and antioxidant properties of the extract.

Evidence strength (skin/topical): Evidence for topical applications is primarily in vitro and based on ingredient-level bioactivity assessments. Robust clinical trial data for S. nigra specifically in skin applications is not currently available in the peer-reviewed literature.

6. Body Systems and Health Areas Associated with Black Willow

Musculoskeletal system: Pain relief in joint and back pain; anti-inflammatory effects in rheumatic conditions (most studied area clinically)
Nervous system: Historical use as a sedative and anaphrodisiac (Eclectic tradition); the plant is described in the homeopathic tradition as primarily affecting the reproductive organs and the nervous system.
Immune/inflammatory system: COX-1 and COX-2 inhibition; TNF-α and NF-kB downregulation documented in vitro
Hepatic/antiviral: In vitro anti-HCV activity (preliminary); broader antiviral activity against coronaviruses and enteroviruses in cell experiments
Integumentary (skin): Exfoliating (salicylic acid precursor), antimicrobial, and anti-inflammatory properties applied in cosmetics
Gastrointestinal system: Condensed tannins provide astringent properties, which may aid in gut lining protection and reduce diarrhea (traditional use; not formally studied in humans for this purpose)
Genitourinary system: Historical Eclectic use for prostatitis, cystitis, ovaritis, and spermatorrhea (no modern clinical evidence)

7. Dosage Forms and Doses Reported in Studies

The most consistently studied dose in human clinical trials of willow bark extract is standardized to salicin content. Typical doses in clinical studies range from 120 to 240 mg of salicin daily.

Low back pain (RCT, Chrubasik et al., 2000): Oral willow bark extract with either 120 mg (low dose) or 240 mg (high dose) of salicin, administered over 4 weeks.
Osteoarthritis (RCT, Schmid et al., 2001): Willow bark extract in a dose corresponding to 240 mg salicin/day, compared with placebo in a 2-week, double-blind, randomized controlled trial.
Osteoarthritis and Rheumatoid Arthritis (RCT, Biegert et al., 2004): Patients received willow bark extract corresponding to 240 mg of salicin/day, diclofenac 100 mg/day, or placebo in a 6-week double-blind trial.
Commercial preparation (Assalix®): A daily dose of 240 mg of salicin has been used in previous studies on participants with osteoarthritis and rheumatoid arthritis; Assalix®, a commercial willow bark preparation, contains 240 mg of salicin per tablet.
Eclectic fluid extract (historical, aments): 20 to 30 minims (1.3–1.8 mL) of the fluidextract four times a day.
Bioavailability note: A salicin content of 240 mg corresponds to approximately 87 mg of acetylsalicylate, which is more cardioprotective than analgesic. The bioavailability of salicin can vary between formulations, a concept applicable to all herbal medications.

8. Safety Considerations and Drug Interactions

General Safety Profile

A 2019 U.S. Pharmacopeia safety review of willow bark found that no serious adverse events were reported from trials of willow bark extracts delivering 120 to 240 mg salicin daily for up to 8 weeks; the trials were conducted in adults only, and none involved children, or pregnant or breastfeeding women; the most common adverse effects associated with willow bark are gastrointestinal, and a few allergic reactions were also reported.

Reports from clinical trials primarily document gastrointestinal discomfort (nausea, stomachache) as well as dizziness and skin rash. While some regulatory bodies suggest limiting willow bark use to 4 weeks, clinical studies and surveys have not found evidence of serious adverse events with use up to 8 weeks, even in large patient groups; no major toxicity or gastrointestinal damage has been observed.

Contraindications

Willow-containing products should be avoided in patients with known hypersensitivity to aspirin, asthma, impaired thrombocyte function, need for vitamin K antagonistic treatment, diabetes, gout, kidney or liver conditions, peptic ulcer disease, and any other medical condition for which aspirin is contraindicated.

There is a risk of increased bleeding in vulnerable individuals; salicylates cross the placenta and are eliminated slowly in newborns; some persons are sensitive or allergic to aspirin; and children are at risk of Reye's syndrome. Children, people who are pregnant or nursing, or people with known sensitivity to aspirin should not use willow bark.

Aspirin Allergy and Cross-Reactivity

In patients with known aspirin allergy, willow bark products are contraindicated. As it contains salicin — a compound related to aspirin — it should be avoided by people allergic to aspirin, those with asthma, ulcers or bleeding disorders, and anyone taking blood-thinning medicines.

Drug Interactions

In general, drug interactions associated with salicylates may apply to willow-containing products; use with alcohol, barbiturates, sedatives, and other salicylate-containing products should be avoided because of potential additive irritant effects, including gastrointestinal tract and platelet function adverse reactions.

Anticoagulants/antiplatelets: The anticoagulant/antiplatelet drug interaction is rated as major ("do not take this combination"); concomitant use theoretically might increase the risk of bleeding due to decreased platelet aggregation; willow bark has antiplatelet effects, but less so than aspirin; concurrent use with anticoagulant and antiplatelet drugs including aspirin, clopidogrel, dalteparin, enoxaparin, heparin, ticlopidine, and warfarin should be avoided.
Warfarin specifically: White willow may enhance the anticoagulant effect of warfarin.
Acetazolamide: Willow bark contains salicin, a plant salicylate; human case reports suggest that a combination of acetazolamide and salicylate can increase unbound plasma levels of acetazolamide, as well as adverse effects related to acetazolamide; theoretically, willow bark might result in additive adverse effects associated with acetazolamide.
Other anti-inflammatory drugs and antihypertensives: Caution is advised when taking anticoagulants, acetazolamide, anti-hypertensives, and anti-inflammatory drugs because willow bark interacts with these drugs.

Platelet Effects and Gastrointestinal Comparison to Aspirin

In contrast to synthetic aspirin, willow bark does not damage the gastrointestinal mucosa; an extract dose with 240 mg salicin had no major impact on blood clotting. Metabolically, willow bark products taken orally are converted in the liver to the active salicylic acid and show fewer side effects in trials than does OTC aspirin; willow bark metabolites have also been shown to inhibit platelet aggregation but to a lesser extent than aspirin.

Reye's Syndrome Risk in Children

Children are at risk of developing Reye's syndrome if exposed to salicylates. Willow bark can interact with certain medications, such as blood thinners and beta-blockers, and even acetaminophen, which in at least one case was associated with the development of Reye's syndrome.

Anaphylaxis

The most common side effects are mild gastrointestinal issues, and a few cases of allergic reactions have been noted, especially in people sensitive to salicylates or aspirin. Rare but serious: in the key low back pain trial, one patient suffered a severe allergic reaction, perhaps to the extract.

Regulatory Status and Labeling Gap

Of 70 willow bark-containing and single-ingredient willow bark products assessed in a PubMed-indexed study, only 8.6% listed any warning; the warning regarding aspirin sensitivity was present on 4.3% of products, Reye's syndrome on 2.9%, and interactions with anticoagulants on 4.3%. Regulatory agencies like the United States Pharmacopeia and the European Medicines Agency recommend cautionary labeling, but these recommendations are not always followed in practice.

References

Health Conditions

Health conditions that Black willow may help support.

No conditions available.

Body Systems

Body systems that Black willow may help support.

No body systems available.