How It Works
Bottom Line: Willow bark may help relieve muscle and joint pain, but it is not an effective weight loss supplement.
Because aspirin is naturally derived from the bark of the willow tree, willow bark is commonly used to treat pain and reduce fevers. In the body, active molecules in willow bark are converted to salicylic acid, the active component of aspirin. 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.
Purported Uses
To reduce fever
Willow bark is thought to act in the same way as aspirin, but no there is no proof from clinical trials 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 osteoathritis. 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, but there is no proof from clinical trials that willow bark can reduce inflammation in humans.
To treat flu
No scientific evidence supports this use.
For weight loss
No scientific evidence supports this use.
Research Evidence
Back pain
A large clinical trial studied the effect of willow bark extract on low back pain. For four weeks, 210 patients were randomly given willow bark extract of two different strengths or a placebo pill. They were allowed to use tramadol as a "rescue" medication if their pain was bad enough. At the end of the study, more patients taking the strongest willow bark extract (240 mg of salicin) reported pain relief (39%) than patients taking the placebo (7%). However, this indicates that willow bark helped less than half of the patients taking it. In addition, more patients in the placebo group needed to take tramadol for pain. This clinical trial gives some support to the use of willow bark for low back pain.
Pain of osteoarthritis
The effect of willow bark extract on the pain of osteoarthritis was assessed in a clinical trial with 78 patients. For two weeks, patients were randomly assigned to receive willow bark containing 240 mg of salicin or a placebo pill. Patients taking willow bark reported a greater decrease in joint pain than those taking placebo, but there was no real difference in their stiffness or ability to get around. These results indicate that willow bark is effective in reducing pain associated with osteoarthritis of the knee or hip.
Warnings
This product is regulated by the FDA as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. This product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Because it can thin the blood, patients should stop taking willow bark two weeks before having surgery to reduce the risk of poor wound healing and excessive bleeding.
Do Not Take If
You are taking warfarin or other blood thinners (In theory, based on the known effects of aspirin, 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).
Side Effects
Rarely, nausea, vomiting, and gastrointestinal bleeding have been reported
Tinnitus (rare)
Kidney damage (rare)
Scientific Name
Common Name
Bay willow, black willow, white willow
Clinical Summary
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. Caution should be exercised in patients with known allergy or intolerance to aspirin or non-steroidal antiinflammatory drugs (NSAIDs). Willow bark should not be administered to children with a fever due to the risk of Reye's syndrome. Adverse reactions are analogous to those seen with aspirin, including gastrointestinal bleeding, nausea, and vomiting. May have additive effect with aspirin and NSAIDs and should therefore not be administered concurrently. Clinical studies demonstrate efficacy of willow bark in the management of back pain and osteoarthritis (7) (8). A systematic review of clinical trials suggests that it may also be effective in treating low back pain (1).
Purported uses
Fever
Headaches
Inflammation
Influenza
Muscle pain
Pain
Weight loss
Constituents
Glycosides: Salicin, salicortin, picein, fragilin, tremulacin and triandrin
Esters of salicylic acid
Tannins
Catechins
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.
(2) (3)
Pharmacokinetics
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.
(5)
Adverse Reactions
Infrequent: Nausea, vomiting, GI bleeding, tinnitus, and renal damage
(4)
Herb-Drug Interactions
No interactions have been reported. However, due to the variable salicylate content found in willow back there are theoretical interactions.
Anticoagulants / Antiplatelets: Theoretically, willow bark may increase the risk of bleeding.
NSAIDs: Theoretically, willow bark may increase the risk of bleeding and GI mucosal damage.
Lab Interactions
Due to the unknown salicylate factor, use caution in interpreting test results that are sensitive to salicylates.
Literature Summary and Critique
References
- 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.
