When most people think about the willow, they envision a tree with long, lazy, and flexible branches perched at the edge of a quiet lake or stream. Willow tree branches have been used for centuries in a wide variety of tasks, from weaving baskets to disciplining children. Medicinally, willow bark is widely used to relieve pain and inflammation.1

Willow bark contains the chemical salicin, which is the precursor to aspirin (acetyl salicylic acid).2 The bark was peeled from the tree trunk, and the ailing person chewed a small piece for relief ofheadaches, fevers, low back pain, and arthritis.1 There are multiple varieties of willow trees, but the most common type found in the United States is the white willow, or Salix alba.1

Science

The active salicin in white willow bark acts primarily as both an analgesic and an antipyretic.3 The actual mechanism of action of salicin is very similar to that of modern prescription medications in the cyclo-oxygenase-1 and 2 (COX-1, COX-2) pathways. Salicin is a nonselective COX-1 and COX-2 inhibitor, effectively acting as an anti-inflammatory by blocking prostaglandin release.3

Metabolically, white willow bark products taken orally are converted in the liver to the active salicylic acid and show fewer side effects in trials than does OTC aspirin.3 White willow bark metabolites also have been show to inhibit platelet aggregation but to a lesser extent than aspirin.4

Using the strength-of-evidence rating scale, white willow bark for arthritis pain gets an “A,” with strong evidence based on quality clinical trials.3 In one small trial of 78 patients, willow bark in a standardized formulation of 60 mg salicin or placebo was given twice daily for 14 days. The treatment group reported significant pain relief, superior to that reported by the placebo group.5

Interestingly, in spite of this rating and several small trials supporting the use of willow bark, other trials failed to show efficacy over placebo or active control.6 These sources and others go as far as to recommend that white willow bark not be used due to both its lack of efficacy and its potential for adverse effects.7

Another ailment closely related to osteoarthritis is chronic low-back pain. The use of white willow bark for this condition earned an evidence level of “B,” meaning it is most likely safe and effective, but more trials need to be done.2 In a randomized controlled trial with a double-blinded, active control, 228 patients with long-term diagnoses of chronic low-back pain were given either a standardized dose of a patented salicin product or a prescription dose of a commercial COX-2 inhibitor. After four weeks, participants’ pain scores were compared with baseline scores. The results showed a nearly identical pain-relief profile and a corresponding lack of serious side effects. The most significant notation, however, may be that the cost of the salicin product was at least 40% less than the COX-2 inhibitor prescription medication.8

Barring a headache with any ominous signs of an emergent condition, tension and migraine headaches have shown varying levels of relief after salicin administration.1 Studies exploring white willow bark’s efficacy for these conditions earned an evidence rating of “C,” indicating marginal supportive data. Adequate clinical trial data supporting white willow’s usefulness in headache management is lacking.9

Safety, side effects, and interaction

The salicylate family of therapies carries the potential for significant GI side effects and anticoagulant action.2 White willow bark preparations, however, appear to be somewhat safer than patented aspirin products: GI side effects of nausea, vomiting, and bleeding are found to occur infrequently.3 Anticoagulant effects of willow bark extracts exist but are of a lower magnitude and length of action than those seen with aspirin and other nonsteroidal anti-inflammatory drugs.3

As with aspirin, allergic reactions to willow bark can occur. These reactions may be mild with a slight rash or severe with asthmatic exacerbations, angioedema, or even anaphylaxis.3

Interactions are similar to those of aspirin. Willow bark extracts can potentiate warfarin and increase GI distress with rare instances of GI bleeding.3 Use in pregnant or nursing women is not recommended, and caution should be used when medicating teens due to the risk of salicylate-induced Reye syndrome.1

Does, how supplied, and cost

White willow bark is available as actual bits of tree bark for chewing, powder, and liquid extract. The cost ranges from $3 for 100 powder-filled capsules to $10 for other formulations. The standard recommended dose in most of the trials noted was from 60 mg to 120mg of actual salicin given with food b.i.d.1

Summary

White willow bark has a very legitimate claim to usefulness. However, there seems to be no convincing data that this substance is a better choice than aspirin. Even though pain relief from willow bark is comparable to that from the more expensive COX inhibitors, it does not provide the pure COX-2 gastric protection. GI risk combined with the real allergy potential and uncertainty in dose forms make white willow bark a poor therapeutic choice.

References

1. University of Maryland Medical Center. Willow bark. 

2. Memorial Sloan-Kettering Cancer Center. Willow bark. 

3. Natural Standard. Willow bark.

4. Natural Medicines Comprehensive Database. Willow bark.

5. Schmid B, Lüdtke 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;15:344-350.

6. Biegert C, Wagner I, Lüdtke 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;31:2121-2130.

7. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, Pa.: Springhouse Corp.; 1999:808-810.

8. Chrubasik S, Künzel 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;40:1388-1393.

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