Natural Products

Willow Bark

Salix alba

Efficacy

• Indications with proven efficacy:
  Back pain
  Fever
  Headache
  Rheumatic ailments
• Indications with possible, but poorly documented efficacy - the use of this product cannot be recommended:
  Ankylosing spondylitis
  Gouty arthritis
  Rheumatoid arthritis

Security

• Risk of Drug Interactions: High
• Adverse Effects: Not Frequent

What is it?

Willow bark is the bark of the white willow, which is indigenous to Europe and North America. The Latin name of this tree was used to name salicylic acid, from which acetylsalicylic acid (Aspirin) was developed. The bark contains several active principles such as glycosides, tannins, flavonoids. Salicilin, the constituent of interest, is first metabolized to saligelin in the digestive tract before being metabolized in salicylic acid upon absorption. Salicin is extracted from the bark of 2 to 3 year-old branches, harvested in early spring. Willow bark is associated with all of the properties of Aspirin. Several species of Salix can be used to collect salicin, but they have highly varying salicin content. Salicine standardized extract should be used.

Warning

In 2004, Canada adopted new regulations that control the manufacturing, packaging, labeling and importing of natural health products. The new regulations also include an adverse reaction reporting system. Products that conform to the regulation's criteria are identified with a natural product number (NPN) or homeopathic medicine number (DIN-HM) and can be legally sold in Canada. This number indicates that the product meets specific criteria for safety and purity, not that it is effective for any indication.

Medicinal plants content varies naturally from plant to plant – just as fruits from the same package may vary in taste and texture. There is no standard to measure the active content of each plant. Thus, efficacy of natural products should be expected to vary from brand to brand as well as from bottle to bottle of the same brand.

For more information about the Natural Health Products Regulations, or to check if a product has been assessed, visit the Health Canada website at http://www.hc-sc.gc.ca/dhp-mps/prodnatur/index-eng.php.

Does it work?

There is evidence that willow bark is effective in the treatment of rheumatic ailments, fever and headaches. It is also used for other indications where it may be of some benefit:

• Rheumatic ailments, fever, headaches:
  A typical dose is 1 to 3 grams bark steeped in boiling water for 5 minutes, 3 to 4 times a day; or the equivalent of 60 to 120 mg of salicin daily.
• Back pain:
  Standardized extract providing 120 to 240 mg of salicin daily has been used. It can take up to one week for significant relief.
• Gouty arthritis, ankylosing spondylitis, rheumatoid arthritis:
  There are no particular dosage recommendations available for these indications. Logically, people should use the same dosage as those used for recognized indications.

Is it safe?

• There are no adverse effects associated with oral willow bark. However, long-term use may result in gastro-intestinal irritation or kidney injury, as seen with salicylate use. Long-term use of willow bark is not advisable, since it may cause peptic ulcers, as seen with Aspirin. However, willow bark does appear safer than Aspirin.
• People allergic to Aspirin should not use willow bark. Although Reye's syndrome has not been reported, administration to children less than 16 years of age is not recommended.
• Since there is no safety data available concerning its use during pregnancy and breast-feeding, pregnant and lactating women should not take willow bark. There are reports of rash in breast-fed infants whose mother used willow bark.
• The risk of drug interaction is not clearly established. Some very cautious experts recommend following the same precautions as with salicylates. Before taking willow bark, check with your pharmacist to make sure that there are no drug interactions with your regular medications.

Clinical notes

• The salicin content of various Salix species is highly variable. Based on a 7% salicin content, someone would have to drink 800 ml of willow bark tea to obtain the equivalent analgesic effect as two Aspirin tablets.

References

1. Blumethal M et al. The Complete German Commission E monographs, 1998
2. Natural Medicines Comprehensive Database, Therapeutic Research Faculty, 2007
3. Lininger S. et Al. The Natural Pharmacy, Prima Health, 1998
4. Barnes J. et Al. Herbal Medicines, 2nd edition, Pharmaceutical Press, 2002
5. Passeportsanté.net. Saule blanc. http://www.passeportsante.net
6. Rotblatt M. et Ziment I. Evidence-Based Herbal Medicine, Hanley & Belfus, 2002