About Herbs

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.

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.

Rare:

Nausea, vomiting, and gastrointestinal bleeding have been reported

Tinnitus

Kidney damage

Bay willow, black willow, white willow

The bark of the willow bark tree contains salicin, the phytotherapeutic precursor of aspirin (acetylsalicylic acid). Clinical studies demonstrate efficacy of willow bark in the management of back pain and osteoarthritis ^{(7) (8)}, gonarthrosis and coxarthrosis ⁽⁹⁾. Conclusions from systematic reviews of clinical trials suggest that it may also be effective in treating low back pain ^{(1) (10)}.
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.

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.
^{(2) (3)}

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⁾

Infrequent: Nausea, vomiting, GI bleeding, tinnitus, and renal damage. ⁽⁴⁾

Warfarin: Willow bark may increase the risk of bleeding ⁽¹¹⁾.
NSAIDs: Theoretically, willow bark may increase the risk of bleeding and GI mucosal damage.

Due to the unknown salicylate factor, use caution in interpreting test results that are sensitive to salicylates.

Few controlled studies have been performed in humans; however, the pharmacological actions of salicylates are well published and applicable to willow bark.

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.
Two hundred and ten patients were randomly assigned to receive an oral willow bark extract with either 120 mg or 240 mg of salicin or placebo, with tramadol as the sole rescue medication in a 4-week blinded trial. Principal outcome measured was proportion of patients who were pain-free without tramadol for at least 5 days during the final week of the study. One hundred and ninety one patients completed the study; the number of pain-free patients in the last week of treatment was 27 (39%) of 65 in the group receiving 240 mg salicin, 15 (21%) of 67 in the group receiving 120 mg salicin and 4 (6.8%) of 59 in the placebo group. Significantly, more patients in the placebo group required tramadol during each week of the study.

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.
Seventy-eight patients were evaluated in this prospective study. Willow bark standardized to 60 mg salicin or placebo was administered as two tablets twice daily for 14 days. A significant decrease in joint pain was reported in the willow bark treatment group as compared to placebo. No significant change in stiffness or physical function was found. Adverse events were comparable between treatment groups. Willow bark was effective in reducing pain associated with osteoarthritis of the knee or hip.