Drugs A - Z
Willow bark (Salix spp.)
Generic Name: Black willow
CategoryHerbs & Supplements
Acetylsalicylic acid, aspirin, Assalix®, Assplant®, basket willow, bay willow, beta-salicin, black willow, brittle willow, cadmium, caffeic acid, crack willow, daphne willow, ecorce de saule (French), ferulic acid, flavonoids, fragilin, glycosides, isosalicin, isosalipurposide, knackweide, laurel willow, lorbeerweide, osier rouge, picein, populin, purple osier, purple osier willow, purple willow, purpurweide, reifweide, rheumakaps, Salicaceae (family), salice (Italian), salicin, salicis cortex, salicortin, salicoylsalicin, salicyl alcohol, salicylate, salicylic acid, salicyluric acid, salidroside, saligenin, salipurposide, Salix alba, Salix daphnoides, Salix fragilis L., Salix pentandra, Salix purpurea L., sauce (Spanish), syringin, tannins, tremulacin, triandrin, vanillin, violet willow, Weidenrinde (German), white willow, white willow bark, willow, willow tree, willowbark, willowprin.
Note: This review covers salicin-containing species of Salix, which includes Salix alba, Salix fragilis, Salix purpurea, and Salix pentandra.
In the United States, willow bark is used by herbalists as an antipyretic (fever reducer), a mild analgesic (pain reliever), and an anti-inflammatory. There is currently strong scientific evidence that willow bark is effective for osteoarthritis and lower back pain. Early study suggests that willow bark extracts may not be helpful for rheumatoid arthritis, but further study is warranted to confirm these recommendations. Taking willow bark may increase the risk of bleeding; however, this risk may be less than taking aspirin.
Several countries in Europe have approved willow bark for pain and inflammatory disorders. The German Commission E has approved willow bark for fever, rheumatic ailments, and headaches. The British Herbal Compendium indicates that willow bark can be used for rheumatic and arthritic conditions, and fever associated with cold and influenza. In France, willow bark has been approved as an analgesic to treat headache and toothache pain, as well as painful articular (joint) conditions, tendonitis, and sprains. The European Scientific Cooperative on Phytotherapy (ESCOP) has approved willow bark extract for the treatment of fever, pain, and mild rheumatic complaints.
EvidenceDISCLAIMER: These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Willow bark is a traditional analgesic (pain relieving) therapy for osteoarthritis. Several studied have confirmed this finding. Additional study comparing willow bark to conventional medicinal agents for safety and effectiveness is warranted.
Lower back pain:
White willow has been compared to placebo and to cyclooxygenase-2 inhibitors, and many of the studies found willow bark to be as effective or superior to other methods. Cost effectiveness studies have also been performed between white willow bark and conventional treatment, and found that willow bark was more cost effective. Additional study would help make a strong recommendation.
Willow bark has traditionally been used to treat an array of inflammatory conditions, including headache. One study investigated a salicin topical cream for the treatment and/or prevention of migraine and tension-type headache. Although early study is promising, additional study is needed to draw a firm recommendation.
There is good evidence that willow bark may be effective in treating chronic pain from osteoarthritis; however, willow bark extract did not show efficacy in treating rheumatoid arthritis. Additional study is needed to make a firm recommendation.
TraditionWARNING: DISCLAIMER: The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.
Analgesic (pain reliever), ankylosing spondylitis (arthritis of the spine), anti-inflammatory, antioxidant, antiplatelet, antipyretic (fever reducer), antiseptic, antiviral, cancer, colds, colorectal cancer, connective tissue disorders, coronary artery disease prevention, diabetes, fever, gout (foot inflammation), headache, inflammation, joint inflammation, labor pain, leukemia, malaria, menstrual cramps, myocardial infarction (heart attack), sore throat, sprains, tendonitis, toothache, warts.
Adults (18 years and older):
The German Commission E monograph (BGA, Commission E) recommends doses of willow bark extract of 60-120 milligrams of total salicin daily. Clinical studies have used 120-240 milligrams willow bark extract (Assalix®) for four weeks to treat lower back pain. For osteoarthritis pain, 1,360-2,160 milligrams willow bark extract containing 240 milligrams of salicin daily for two weeks has been found effective.
Children (younger than 18 years):
There is no proven safe or effective dose for willow bark in children. Due to the potential for Reye's syndrome from salicylates, children with influenza, varicella (chickenpox), or any suspected viral infection should avoid willow bark.
SafetyDISCLAIMER: Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
Avoid in individuals with a known allergy or hypersensitivity to aspirin, willow bark (Salix species), or any of its constituents, including salicylates. Symptoms of allergy may include swollen eyes, pruritus (itching), eczema, anaphylaxis, cough, hoarseness, and dysphonia (abnormal voice).
Side Effects and Warnings
Willow bark extract has been reported to cause various gastrointestinal problems, headaches, and allergic reactions. Plants containing salicylates have a very bitter taste, so willow bark tea may be unpalatable (unpleasant) for most patients, particularly for children.
Side effects of willow bark may include blood pressure instability, edema (swelling), rash, Hypertriglyceridemia (an excess of triglycerides in the blood), diarrhea, heartburn, vomiting, and dyspepsia (upset stomach). Willow bark may also lead to hyperuricemia (high levels of uric acid in the blood), which may precipitate an attack of gout in susceptible patients. Willow bark may cause hepatic dysfunction, dizziness, fatigue, swollen eyes, bronchospam, papillary necrosis or headaches.
Although not well studied in humans, combination products containing willow may cause acute weakness, hematemesis (blood in the vomit), melena (black stools), abdominal pain, pale mucous membranes, and panhypoproteinemia (low levels of protein in the blood), indicating severe gastrointestinal bleeding.
The salicylates present in willow bark may also impair platelet function resulting in an increased bleeding time. However, daily consumption of salicis cortex extract is thought to affect platelet aggregation to a far lesser extent than acetylsalicylate. Caution is advised in patients with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
Pregnancy and Breastfeeding
Willow bark is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence. Salicylates are listed as a pregnancy category D; there is positive evidence of human fetal risk with use. Salicylates in breast milk may cause rash in breastfed babies.
Interactions with Drugs
Use of acetazolamide and salicylates may cause lethargy, incontinence, and confusion. Caution is advised in patients taking acetazolamide, a carbonic anhydrase inhibitor, which is often used in treating glaucoma or acute mountain sickness. Taking carbonic anhydrase inhibitors with willow bark may increase the therapeutic and toxic effects of both the carbonic anhydrase inhibitor and the salicylate.
Salicis cortex extract may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®). Willow bark may also have anti-inflammatory effects. When willow bark is taken in combination with sulfinpyrazone, it may theoretically result in additive anti-platelet effects, which may increase bleeding time.
Willow bark extract may induce hypertriglyceridemia (excess of triglycerides in the blood) or cause blood pressure instability. Patients taking blood pressure medications should consult with a qualified healthcare professional, including a pharmacist. Monitoring may be necessary. Theoretically, the concomitant use of beta-blockers with willow bark may impair the effectiveness of beta-blockers due to willow bark's proposed aspirin-like pharmacological actions.
Theoretically, the concomitant use of diuretics with willow bark may reduce the effectiveness of diuretics and may enhance the risk for salicylic acid toxicity. White willow may also decrease the renal (kidney) excretion of methotrexate resulting in toxic levels due to its salicin content.
Theoretically, the concomitant use of phenytoin (Dilantin®) with willow bark's salicylates may increase the Dilantin® levels in the blood, resulting in toxicity.
Theoretically, the concomitant use of probenecid with willow bark may impair the effectiveness of probenecid.
Due to the plasma protein-binding salicylate component of white willow bark, some other plasma protein-bound drugs may be displaced, possibly resulting in altered drug levels. Consult with a qualified healthcare professional, including a pharmacist, for a full list of these agents.
Willow bark plus spironolactone may result in antagonistic or additive effects.
Theoretically, the concomitant use of sulfonylureas with willow bark may increase the effect of sulfonylureas, possibly increasing the side effects and toxicity.
Theoretically, white willow bark may impair the effectiveness of valproic acid.
Interactions with Herbs and Dietary Supplements
Willow bark extract may induce hypertriglyceridemia (excess of triglycerides in the blood) or cause blood pressure instability. Patients taking herbs and supplements that affect blood pressure or cholesterol should use willow bark cautiously.
Willow bark may be contaminated with high levels of cadmium, which may increase concentrations of cadmium in the body. Consumers should select tested brands to avoid using contaminated products.
Theoretically, the concomitant use of diuretics (increases urine flow) herbs or supplements with willow bark may reduce the effectiveness of the diuretic and may enhance the risk for salicylic acid toxicity. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.
Willow bark may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
Willow bark may have anti-inflammatory effects and may interact positively with guaiacum resin, black cohosh, sarsaparilla, and poplar bark to reduce chronic arthritic pain symptoms.
The concomitant administration of tannin-containing herbs or supplements may result in the malabsorption of salicylic acid.
This information is based on a systematic review of scientific literature, and was peer-reviewed and edited by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com): Heather Boon, BScPhm, PhD (University of Toronto); Cynthia Dacey, PharmD (Natural Standard Research Collaboration); Jessica Clubb, PharmD (Northeastern University); Molly Davis, PharmD (University of Rhode Island); Antoinette Edmondson, PharmD (Massachusetts College of Pharmacy); Nicole Giese, MS (Natural Standard Research Collaboration); Mary McGarry, RPh (University of Kansas); Son Le, PharmD (Massachusetts College of Pharmacy); William Nguyen, PharmD (Massachusetts College of Pharmacy); Anabela Santos, PharmD (Northeastern University); Susanne Schadde, MD; Shaina Tanguay-Colucci, BS (Natural Standard Research Collaboration); Catherine Ulbricht, PharmD (Massachusetts General Hospital), Wendy Weissner, BA (Natural Standard Research Collaboration).
BibliographyDISCLAIMER: Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.
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Schmid B, Ludtke R, Selbmann HK, et al. Efficacy and tolerability of a standardized willow bark extract in patients with osteoarthritis: randomized placebo-controlled, double blind clinical trial. Phytother Res 2001;15(4):344-350.
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Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.