- Indications with possible efficacy:
- Indications with possible, but poorly documented efficacy
- Risk of Drug Interactions: High
- Adverse Effects: Not Frequent
Part of the plant used: bark
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.
Direction of use
- Osteoarthritis and back pain:
It can take up to one week for significant relief.
Tea - 1 to 3 grams bark steeped in boiling water for 5 minutes, 3 to 4 times a day.
Standardized salicin extract - 60 mg 1 to 4 times daily. Better results have been seen with a daily dose of 240 mg.
- Side effects
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, particularly if chronic use or high doses. However, willow bark does appear safer than Aspirin.
People allergic to Aspirin or suffering from renal dysfunction 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.
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.
- Pregnancy and breastfeeding
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 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.
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) 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 plant contents vary 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 www.hc-sc.gc.ca/dhp-mps/prodnatur/index-eng.php.
- Blumethal M et al. The Complete German Commission E monographs, 1998
- Natural Medicines Comprehensive Database, Therapeutic Research Faculty, 2010
- Lininger S. et Al. The Natural Pharmacy, Prima Health, 1998
- Barnes J. et Al. Herbal Medicines, 2nd edition, Pharmaceutical Press, 2002
- Passeportsanté.net. Saule blanc. www.passeportsante.net
- Rotblatt M. et Ziment I. Evidence-Based Herbal Medicine, Hanley & Belfus, 2002
- The Review of Natural Products, 6th Edition, 2010
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The patient information leaflets are provided by Vigilance Santé Inc. This content is for information purposes only and does not in any manner whatsoever replace the opinion or advice of your health care professional. Always consult a health care professional before making a decision about your medication or treatment.