The willow (Salix spp.) is a large tree with thin, hanging branches that bear slender leaves and flower clusters called catkins. The bark and leaves were used to make an anti-inflammatory, pain-relieving medicine in ancient Mesopotamia, Babylon, Sumeria, Egypt, China and Greece. You will find willow listed in the Edwin Smith Papyrus amongst the clinical cases, where it was used to treat a surgical wound to the breast by applying it as a poultice.¹ Hippocrates knew the willow and recommended chewing the bark for treating fever  and to assist child birth, and it is listed in Dioscorides for treating several complaints including intestinal obstruction and gout.²

White willow (Salix alba) is a versatile herb and the bark or leaves can be used to treat many complaints in the form of an infusion, decoction, alcohol tincture or cream. Apart from fevers and colds, it has been used to treat the pain or irritations of arthritis, rheumatism, headaches, stomach upsets, sore throats, gout, eczema, wounds, burns, enlarged prostates and urinary tract infections.

The bark and leaves contain phenolic compounds called salicylates which are responsible for the antipyretic and anodyne activity when metabolised in the digestive system. After absorption, salicylates are hydrolysed in the intestine then oxidised to salicylic acid, a substance which inhibits cyclooxygenase enzymes (COX-1,2) involved in inflammatory prostaglandin synthesis.

This substance also has an irritant action on the mucus membranes when used in isolation from the whole plant, which also contains fibre, flavonoids, polyphenols and procyanidins that exert a protective effect on mucus membranes. Some of these substances, found in both the bark and leaves, exhibit strong antioxidant activity.³

Salicylates (salicin) were first isolated from willow bark and meadowsweet in the early nineteenth century. They were later synthesised at a much cheaper cost in the form of sodium salicylate which enabled industrial-scale production; however, this substance produced serious side-effects. Chemists at the German company Bayer solved this problem when they synthesised the related compound acetylsalicylic acid, which has less irritant action, from acetylchloride and sodium salicylate. They marketed it as Aspirin in 1899.

The synthesis of this substance in the laboratory removed the necessity to use actual plant material in the production of aspirin, and so enabled a global industry to develop. This industry still produces tens of thousands of tons of aspirin per year despite the discovery of other modern anti-inflammatory medicines such as acetaminophen (Panadol).⁴ Unfortunately, aspirin can still cause side-effects such as tinnitus, stomach bleeding, Rayne’s syndrome in children, and is a leading cause of peptic ulcer when used long term.

In another example of the development of alternative anti-inflammatory drugs, a clinical trial for treating back pain found that willow bark is equivalent in effect to the new generation COX-2 inhibitor called Vioxx. This modern drug was produced at huge expense due to the necessity for thorough clinical testing, but was withdrawn soon after its release due to side-effects such as an increased risk of heart attack.⁵ A glance in the doctor’s fat compendium of drugs, The Monthly Index of Medical Specialities (MIMS), will inform even a casual reader that synthetic modern drugs are in fact plagued by a bewildering array of side-effects, albeit categorised rather helpfully as common or rare.

Nevertheless, you may also experience an adverse reaction to the salicylates present in white willow or meadowsweet. In fact salicylates are found in many other fruits, vegetables and drinks and may be the cause of salicylate intolerance. They occur in apples, cherries, cranberries, strawberries, currants, raisins, kiwi, peaches, nectarines, asparagus, corn, tomatoes, curry powder, cinnamon, fenugreek, mint, nutmeg, rosemary, thyme, turmeric, licorice, honey, coffee, pineapple juice and cider.

Salicylate intolerance is classified as a ‘nonspecific antigen-induced pseudo-allergic hypersensitivity reaction to salicylic acid’. This condition is estimated to occur at a rate of about  2.5% in Europe with 20% of asthmatics affected, and 2-7% of people suffering with irritable bowel disease.⁶ Symptoms can be systemic or local in manifestation, and the classic acute ones are itching, urticaria, swelling, colic, an altered bowel habit and asthma attacks. The chronic symptoms are bronchitis, sinusitis and the development of nasal polyps.⁷

Disclaimer:

This article is intended for the purpose of general education only, and is not a substitute for a diagnosis, treatment advice, or a prescription given in a consultation with a qualified physician.

References:

1.         Breasted J. The Edwin Smith Surgical Papyrus. Chicago: The Uni Chicago Press; 1930.

2.         Dioscorides P. De Materia Medica. South Africa: Ibidis; 2000.

3.         Piątczak E, Dybowska M, Płuciennik E, Kośla K, Kolniak-Ostek J, Kalinowska-Lis U. Identification and accumulation of phenolic compounds in the leaves and bark of Salix alba (L.) and their biological potential. Biomolecules 2020;10.

4.         Mackowiak PA. Brief history of antipyretic therapy. Clin Infect Dis 2000;31 Suppl 5:S154-156.

5.         Chrubasik S, Künzel O, Model A, Conradt C, Black A. 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;40:1388–93.

6.         Skypala IJ, Williams M, Reeves L, Meyer R, Venter C. Sensitivity to food additives, vaso-active amines and salicylates: a review of the evidence. Clin Transl Allergy 2015;5:34.

7.         Raithel M, Baenkler HW, Naegel A, et al. Significance of salicylate intolerance in diseases of the lower gastrointestinal tract. J Physiol Pharmacol 2005;56 Suppl 5:89–102.