Salicaceae

Salix alba

White willow

Trial support Caution Yielded a drug

Part used: bark
Native range: Europe, western and central Asia, north Africa
Morphology: A large deciduous tree to twenty-five metres, with narrow leaves silvery-white beneath, which is where the name comes from.

What is in it

phenolic glycosides salicin, salicortin

flavonoids

tannins

Evidence

Willow bark extract has modest trial support for low back pain and osteoarthritis, generally at doses that deliver meaningful quantities of salicin. The effect is smaller and slower than an equivalent aspirin dose.

Safety

Shares aspirin risk. Gastrointestinal irritation and bleeding, and the same caution against use in children and adolescents with viral illness because of Reye syndrome. Contraindicated in salicylate allergy and in asthma sensitive to aspirin.

Interactions: Additive bleeding risk with anticoagulants and antiplatelets; Additive with other NSAIDs

How the traditions classify it

Galenic Classed as cold and dry. Dioscorides records willow leaves and bark for pain and for fever.

Chinese Related willow species are used, described as cold and bitter, for heat and pain.

Three systems, rating the same plant. Where they disagree, none of them is correcting the others — they are separate frameworks that arrived at their categories independently.

Historical use

Among the oldest recorded analgesics. Sumerian and Egyptian sources mention willow for pain; Hippocratic writings and Dioscorides record it for fever and inflammation. English clergyman Edward Stone reported a systematic trial of willow bark for ague to the Royal Society in 1763.

Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.

Worth knowing

Willow is the origin story of the most widely used drug in the world, and the details are more instructive than the headline.

Salicin is a prodrug: the body converts it to salicylic acid. Salicylic acid works and is hard on the stomach, which is why Felix Hoffmann at Bayer acetylated it in 1897 to make acetylsalicylic acid. The chemistry was not a betrayal of the tradition, it was a fix for the tradition's known problem.

Edward Stone deserves more attention than he gets. In 1763 he reported giving powdered willow bark to fifty people with fever and recording the results — a small clinical trial, conducted by a country parson, twenty years before Withering did the same for foxglove.

Nomenclature verified against GBIF backbone taxonomy.