Willow Bark

Willow Bark

Willow Bark

Common Names

  • Bay willow
  • Black willow
  • White willow

For Patients & Caregivers

Willow bark is useful in relieving muscle and joint pain, but may have side effects similar to aspirin.

Willow bark is commonly used to treat pain and reduce fevers. It contains a compound called salicin that has been shown to have anti-inflammatory effects. Several studies have shown that willow bark extracts are effective in reducing back pain and osteoarthritis.

Although aspirin is developed from salicin, a direct comparison between aspirin benefits and willow bark benefits cannot be made. At the same time, aspirin-like side effects may occur with willow bark.

  • To reduce fever
    Willow bark is thought to act in a similar way as aspirin, but clinical trials have not been performed.
  • To treat pain, including muscle and joint pain
    Clinical trials have shown that willow bark extract is effective in treating low back pain. Other study results are mixed for its ability to relieve osteoarthritis pain.
  • To aid in weight loss
    There are no studies to indicate that willow bark can aid in weight loss, and a case report of allergic reaction in someone who used a weight-loss product with willow bark.

Due to possible bleeding complications, willow bark should be discontinued before surgery or chemotherapy.
Individuals with impaired platelet function should also avoid willow bark, as it may interfere with blood clotting.

  • 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): Willow bark may increase the risk of stomach and intestinal damage and bleeding.
  • You have sensitivity to aspirin or aspirin-containing products.
  • You have asthma, breathing problems, chest tightness, or throat tightness.
  • You have stomach problems or an ulcer.
  • You are having skin rash, hives, or itchy / swollen skin.
  • Stomach or intestinal discomfort, allergic reaction, sudden rash, or itching
  • May prevent blood clotting or cause bleeding problems

Case reports:

  • Serious allergic reaction in a 25-year-old woman with a history of allergy to aspirin products. The product used was a supplement promoted for weight-loss that contained willow bark.
  • Acute breathing distress in a 61-year-old woman who suddenly became short of breath and coughed repeatedly after taking willow bark.
  • Children should not be given willow bark because of the potential for developing Reye syndrome, a serious condition associated with the use of aspirin.

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For Healthcare Professionals

Salix alba, Salicis cortex

Willow is a deciduous tree native to Europe, Asia and some parts of North America. Its bark has been used for thousands of years in China and Europe as a remedy for fevers and pain.

Willow bark extracts exert anti-inflammatory (1), antiplatelet (2), and antiproliferative (3) effects in vitro.

Clinical studies indicate that willow bark may help manage back pain (5)(6), although studies of osteoarthritis are mixed (7)(8)(9), and possibly negative for rheumatoid arthritis (6)(9). Topical application of salicin may help reduce skin aging (10).

In vitro and animal models suggest that salicin in willow bark has antitumor and antiangiogenic effects (4).

Aspirin, a drug derived from salicin, has been studied for the prevention of cardiovascular diseases as well as cancer (21). However, willow bark should not be used as a substitute for aspirin because of the variation in its potency. Children should not be given willow bark because of the potential for developing Reye syndrome, a serious condition associated with the use of aspirin (22).

  • Arthritis
  • Fever
  • Headaches
  • Inflammation
  • Influenza
  • Pain
  • Weight loss

Although anti-inflammatory activity is mostly attributed to salicin (13), a main bioactive compound in willow bark, catechol and flavonoid compounds have also been found to be responsible (12). Willow bark inhibits pro-inflammatory cytokines (tumor necrosis factor [TNF]-alpha), cyclo-oxygenase (COX)-2, and nuclear translocation of the transcription factor NF-κB (1). It was also found to significantly raise low glutathione (GSH) levels, thereby limiting lipid peroxidation (14).

Antiproliferative effects on human colon and lung cancer cells are due to growth-inhibition and apoptotic induction (15). In vitro and animal models suggest salicin can inhibit reactive oxygen species (ROS) and extracellular signal-regulated kinase (ERK) signaling pathways to produce antiangiogenic effects (4).

Due to potential for bleeding complications (16), willow bark should be discontinued before surgery or chemotherapy.
Those with impaired thrombocyte function should avoid willow bark, as it may interfere with blood clotting (2).

Allergy or sensitivity to salicylates such as aspirin.

Gastrointestinal discomfort; allergic reaction, erythema, pruritus (sudden rash, itching) (5)(7)(17).
May inhibit platelet aggregation or cause bleeding complications (2)(16).
Anaphylaxis: In a 25-year-old woman with a history of allergy to acetylsalicylic acid, from the use of a supplement promoted for weight-loss that contained willow bark (18).
Acute respiratory distress syndrome: In a 61-year-old woman with history of hypertension and osteoarthritis after taking a willow bark supplement. Symptoms included sudden dyspnea and non-productive cough, and there was no history of drug or supplement allergy (19).

Warfarin or other anticoagulants: When used concurrently, willow bark may increase the risk of bleeding (20).


  1. Krivoy N, Pavlotzky E, Chrubasik S, et al. Effect of salicis cortex extract on human platelet aggregation. Planta Med. Apr 2001;67(3):209-212.

  2. Bonaterra GA, Kelber O, Weiser D, et al. In vitro anti-proliferative effects of the willow bark extract STW 33-I. Arzneimittelforschung. 2010;60(6):330-335.

  3. 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. Jul 2000;109(1):9-14.

  4. Vlachojannis JE, Cameron M, Chrubasik S. A systematic review on the effectiveness of willow bark for musculoskeletal pain. Phytother Res. Jul 2009;23(7):897-900.

  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. Sep 2010;9(3):196-201.

  6. Freischmidt A, Jurgenliemk G, Kraus B, et al. Contribution of flavonoids and catechol to the reduction of ICAM-1 expression in endothelial cells by a standardised Willow bark extract. Phytomedicine. Feb 15 2012;19(3-4):245-252.

  7. Fuster V, Sweeny JM. Aspirin: a historical and contemporary therapeutic overview. Circulation. Feb 22 2011;123(7):768-778.

  8. Khayyal MT, El-Ghazaly MA, Abdallah DM, et al. Mechanisms involved in the anti-inflammatory effect of a standardized willow bark extract. Arzneimittelforschung. 2005;55(11):677-687.

  9. Hostanska K, Jurgenliemk G, Abel G, et al. Willow bark extract (BNO1455) and its fractions suppress growth and induce apoptosis in human colon and lung cancer cells. Cancer Detect Prev. 2007;31(2):129-139.

  10. Maroon JC, Bost JW, Maroon A. Natural anti-inflammatory agents for pain relief. Surg Neurol Int. 2010;1:80.

  11. Boullata JI, McDonnell PJ, Oliva CD. Anaphylactic reaction to a dietary supplement containing willow bark. Ann Pharmacother. Jun 2003;37(6):832-835.

  12. Srivali N, Cheungpasitporn W, Chongnarungsin D, et al. White willow bark induced acute respiratory distress syndrome. N Am J Med Sci. May 2013;5(5):330.

  13. Brotons C, Benamouzig R, Filipiak KJ, Limmroth V, Borghi C. A Systematic Review of Aspirin in Primary Prevention: Is It Time for a New Approach? Am J Cardiovasc Drugs. 2014 Dec 12. [Epub ahead of print]

  14. Beutler AI, Chesnut GT, Mattingly JC, Jamieson B. FPIN’s Clinical Inquiries. Aspirin use in children for fever or viral syndromes. Am Fam Physician. 2009 Dec 15;80(12):1472.

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