Willow bark (Salix spp.)
Natural Standard Bottom Line Monograph, Copyright © 2013 (www.naturalstandard.com). Commercial distribution prohibited. This monograph is intended for informational purposes only, and should not be interpreted as specific medical advice. You should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.
While some complementary and alternative techniques have been studied scientifically, high-quality data regarding safety, effectiveness, and mechanism of action are limited or controversial for most therapies. Whenever possible, it is recommended that practitioners be licensed by a recognized professional organization that adheres to clearly published standards. In addition, before starting a new technique or engaging a practitioner, it is recommended that patients speak with their primary healthcare provider(s). Potential benefits, risks (including financial costs), and alternatives should be carefully considered. The below monograph is designed to provide historical background and an overview of clinically-oriented research, and neither advocates for or against the use of a particular therapy.
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.
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.
*Key to grades:A: Strong scientific evidence for this use; B: Good scientific evidence for this use; C: Unclear scientific evidence for this use; D: Fair scientific evidence against this use (it may not work); F: Strong scientific evidence against this use (it likely does not work).
The below uses are based on tradition or scientific theories. 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 health care professional.
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.
The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
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.
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
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, an excess of triglycerides in the blood, diarrhea, heartburn, vomiting, and dyspepsia (upset stomach). Willow bark may also lead to 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, blood in the vomit, black stools, abdominal pain, pale mucous membranes, and 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.
Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.
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.
The combination of salicin, which is found in willow bark, and alcohol may increase the risk of gastrointestinal bleeding and gastritis.
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 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 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 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 edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
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.
Baker S, Thomas PS. Herbal medicine precipitating massive haemolysis. Lancet 5-2-1987;1(8540):1039-1040. View Abstract
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. J.Rheumatol. 2004;31(11):2121-2130. View Abstract
Chrubasik S, Künzel O, Model A, et al. Assalix® vs. Vioxx® for low back pain - a randomised open controlled study. 8th Annual Symposium on Complementary Health Care, 6th - 8th December 2001 2001.
Chrubasik S, Eisenberg E, Balan E, et al. Treatment of low back pain exacerbations with willow bark extract: a randomized double-blind study. Am J Med 2000;109(1):9-14. View Abstract
Chrubasik S, Kunzel O, Black A, et al. Potential economic impact of using a proprietary willow bark extract in outpatient treatment of low back pain: an open non-randomized study. Phytomedicine 2001;8(4):241-251. View Abstract
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 (Oxford) 2001;40(12):1388-1393. View Abstract
Edwards JE, Oldman A, Smith L, et al. Single dose oral aspirin for acute pain. Cochrane Library 2002;1.
Eisenberg E, Chrubasik S, Balan E, et al. Willow bark extract for low back pain: a randomised double-blind study. Focus on Alternative and Complementary Therapies 2002;7(1):91-92.
Ernst E, Chrubasik S. Phyto-anti-inflammatories. A systematic review of randomized, placebo- controlled, double-blind trials. Rheum Dis Clin North Am 2000;26(1):13-27, vii. View Abstract
Gagnier JJ, van Tulder M, Berman B, Bombardier C. Herbal medicine for low back pain. Cochrane Database.Syst.Rev 2006;(2):CD004504. View Abstract
Hyson MI. Anticephalgic photoprotective premedicated mask. A report of a successful double-blind placebo-controlled study of a new treatment for headaches with associated frontalis pain and photophobia. Headache 1998;38:475-477.
Little CV, Parsons T, Logan S. Herbal therapy for treating osteoarthritis. The Cochrane Library 2002;1.
Marson P, Pasero G. [The Italian contributions to the history of salicylates]. Reumatismo. 2006;58(1):66-75. View Abstract
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. View Abstract
Schmid B, Ludtke R, Selbmann HK, et al. [Effectiveness and tolerance of standardized willow bark extract in arthrosis patients. Randomized, placebo controlled double-blind study]. Z Rheumatol 2000;59(5):314-320. View Abstract
Copyright © 2013 Natural Standard (www.naturalstandard.com)
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.
March 22, 2017