Health Care Professional Information
Bay willow, black willow, white willow
Derived from the bark of the tree, willow bark contains salicin, the phytotherapeutic precursor of aspirin (acetylsalicylic acid). Products should be standardized to the content of salicin with daily doses ranging from 60-120 mg per day. In vitro studies show that willow bark has anti-inflammatory (14) and antiproliferative (15) effects.
Clinical studies demonstrate its efficacy in the management of back pain and osteoarthritis (7) (8), and a systematic review suggests it may also be effective in treating low back pain (1) (10), gonarthrosis and coxarthrosis (9). Topical application of salicin may help reduce aging of the skin (16).
Adverse reactions are analogous to those seen with aspirin, including gastrointestinal bleeding, nausea, and vomiting. May have additive effects with aspirin and NSAIDs, and should therefore not be administered concurrently. Caution should be exercised in patients with known allergies or intolerance to aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) (17). Willow bark should not be administered to children with fever due to the risk of Reye's syndrome.
- Muscle pain
- Weight loss
- Glycosides: Salicin, salicortin, picein, fragilin, tremulacin and triandrin
- Esters of salicylic acid
- Flavonoids (6)
Mechanism of Action
All the phenolic glycosides of willow bark have similar physiological and pharmacological effects. In the intestinal tract and the liver, the phenolic glycosides convert to the active principle, salicylic acid. Because of the time required for this conversion, the therapeutic properties of willow bark are expressed more slowly but continue to be effective for a longer time than if salicylate itself were administered. The tannins have astringent properties, and in vitro tests show that salicin and salicortin inhibit cyclooxygenase, and an irreversible inhibition of thrombocytes is unlikely. Therefore, no increased interaction with anticoagulants should occur.
In a pharmacokinetic study in humans, three tablets containing willow bark (standardized to a total dose of 55 mg salicin) were administered to 12 male volunteers in three doses over a period of eight hours. The calculated half-life of salicin in the plasma was approximately 2.5 hours.
Patients with known allergies or intolerance to aspirin should not take willow bark (17).
Infrequent: Nausea, vomiting, gastrointestinal bleeding, tinnitus, and renal damage (4) (12).
Willow bark supplements can affect platelet aggregation (13).
Warfarin: Willow bark may increase the risk of bleeding (11).
NSAIDs: Theoretically, willow bark may increase the risk of bleeding and GI mucosal damage.
Herb Lab Interactions
Due to the unknown salicylate factor, use caution in interpreting test results that are sensitive to salicylates.
Literature Summary and Critique
Dosage (Inside MSKCC Only)
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- Gagnier JJ, van Tulder MW, Berman B, et al. Herbal medicine for low back pain. Spine 2007;32(1):82-92.
- Tyler V. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Binghamton: Pharmaceutical Press; 1994.
- Wichtl MW. Herbal Drugs and Phytopharmaceuticals. Boca Raton: Medpharm Scientific Publ; 1994.
- Schulz, et al. Rational Phytotherapy: A Physicians Guide to Herbal Medicines, 3rd ed. Berlin (Germany): Springer; 1996.
- Blumenthal, et al. Herbal Medicine Expanded Commission E Monographs, 1st ed. Austin: American Botanical Council; 2000.
- Newall CA, et al. Herbal Medicines: Guide for Health-Care Professionals, 1st ed. London: Pharmaceutical Press; 1998.
- Chrubasik S, et al. Treatment of low back pain exacerbations with willow bark extract: a randomized double-blind study. Am J Med 2000;109:9-14.
- Schmid B, 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;15:344-50.
- Beer AM, Wegener T. Willow bark extract (Salicis cortex) for gonarthrosis and coxarthrosis - Results of a cohort study with a control group. Phytomedicine. 2008 Sep 22. [Epub ahead of print].
- Vlachojannis JE, Cameron M, Chrubasik S. A systematic review on the effectiveness of willow bark for musculoskeletal pain. Phytother Res. 2009 Jul;23(7):897-900. Review.
- Shalansky S, Lynd L, Richardson K, et al. Risk of warfarin-related bleeding events and supratherapeutic international normalized ratios associated with complementary and alternative medicine: a longitudinal analysis. Pharmacotherapy. 2007 Sep;27(9):1237-47.
- Rohner Mächler M, Glaus TM, Reusch CE. [Life threatening intestinal bleeding in a Bearded Collie associated with a food supplement for horses].Schweiz Arch Tierheilkd. 2004 Oct;146(10):479-82.
- Krivoy N, Pavlotzky E, Chrubasik S, et al. Effect of salicis cortex extract on human platelet aggregation. Planta Med. 2001 Apr;67(3):209-12.
- Bonaterra GA, Heinrich EU, Kelber O, et al. Anti-inflammatory effects of the willow bark extract STW 33-I (Proaktiv(®)) in LPS-activated human monocytes and differentiated macrophages. Phytomedicine. 2010 Dec 1;17(14):1106-13.
- Bonaterra GA, Kelber O, Weiser D, Metz J, Kinscherf R. In vitro anti-proliferative effects of the willow bark extract STW 33-I. Arzneimittelforschung. 2010;60(6):330-5.
- Gopaul R, Knaggs HE, Lephart JF, et al. An evaluation of the effect of a topical product containing salicin on the visible signs of human skin aging. J Cosmet Dermatol. 2010 Sep;9(3):196-201.
- Vlachojannis J, Magora F, Chrubasik S. Willow Species and Aspirin: Different Mechanism of Actions. Phytother Res. 2011 Jan 12. [Epub ahead of print]
How It Works
Bottom Line: Willow bark may help relieve muscle and joint pain.
Willow bark is commonly used to treat pain and reduce fevers. In the body, substances in willow bark are converted to salicylic acid, an aspirin-like compound. Because of the time it takes for this conversion to take place, scientists have found that the effects of willow bark take a longer time to appear, but last longer than aspirin. Salicylic acid halts an important step in the inflammatory process, which is why it can reduce swelling. It is not yet known whether willow bark has the same anticoagulant effects as aspirin in humans.
- To reduce fever
Willow bark is thought to act in the same way as aspirin, but no clinical trials have been performed to confirm that this herb can reduce fever.
- To treat pain, including muscle pain and headaches
Two clinical trials have shown that willow bark extract is effective in treating low back pain, and one clinical trial suggested that it can reduce the pain of osteoarthritis. Another clinical trial found that it could reduce pain in patients with gonarthritis (arthritis of the knee) and coxarthrosis (arthritis of the hip joint). No other clinical trials have evaluated this use.
- To reduce inflammation
Willow bark is converted to salicylic acid in the body; salicylic acid is known to halt the inflammatory process. However, willow bark has not been tested in clinical trials to see if it can reduce inflammation in humans.
- Because it has blood-thinning property, willow bark should not be taken two weeks before surgery to reduce the risk of poor wound healing and excessive bleeding.
Do Not Take If
- You are taking warfarin or other blood thinners (Willow bark may increase the risk of bleeding).
- You are taking non-steroidal anti-inflammatory drugs (NSAIDs) (In theory, based on the known effects of aspirin, willow bark may increase the risk of stomach and intestinal damage and bleeding).
- You are allergic to aspirin.
- Nausea, vomiting, and gastrointestinal bleeding have been reported.
- Tinnitus (rare)
- Kidney damage (rare)
- Willowbark supplements can affect platelet aggregation.
Last updated: October 4, 2011