While white willow (Salix alba) is the willow species most commonly used for medicinal purposes, crack willow (S. fragilis), purple willow (S. purpurea), and violet willow (S. daphnoides) are all salicin-rich and are sometimes sold under the label of willow bark.
Botanical Name / Family
Salix alba (family Salicaceae)
Plant Part Used
Phenolic glycosides, mainly salicylates including salicin and its derivatives, tannins, mainly catechin tannins, some gallontannins and condensed tannins (procyanidins), and flavonoids.
This herb has been used as a therapeutic agent since ancient times, with some reports stating that it was used in ancient China around 500 BC as a treatment for pain and fever and around 400 BC by Hippocrates, who recommended the bark be chewed for relief of fever and pain. As centuries passed, herbalists continued to prescribe the bark for many conditions and by the 18th century, it was widely used as an antipyretic and analgesic. Sometime during the late 1820s, French and German scientists extracted the glycosidic constituents, including salicin. The oxidation of salicin yields salicylic acid, which was produced in the mid 1800s but had limited clinical use due to the gastric irritation it caused. In 1853 a French chemist neutralised salicylic acid to create acetylsalicylic acid, but had no interest in marketing it and abandoned his discovery. A Bayer chemist called Hoffmann rediscovered acetylsalicylic acid in 1897 as a better tolerated treatment for his father’s RA and within 2 years it was marketed by Bayer under the tradename of Aspirin. Since then it has become one of the most successful medicines in history. Although many believe aspirin was synthesised from the salicin found in willowbark, it was actually the salicin found in another herb, meadowsweet, from which aspirin was developed.
Willowbark: Main Actions
Clinical studies using willowbark preparations standardised to salicin content have shown anti-inflammatory and analgesic activity. In vitro studies have demonstrated that Sa/ix extract inhibits COX-2-mediated PGE2 release and that it is a weak inhibitor of proinflammatory cytokines. While salicin is considered the main analgesic constituent, it is now thought that other constituents such as tannins, flavonoids, and salicin esters may contribute to its overall effect.
Clinical note — Lack of significant haemotological effects
It has largely been assumed that willowbark alters platelet aggregation and increases bleeding time, in much the same way as aspirin. Whether this is in fact correct and clinically significant has been investigated by Krivoy et al (2001). The clinical study found that consumption of Salicis cortex extract (containing 240 mg salicin per daily dose) only minimally affected platelet aggregation compared with a cardioprotective dose of acetylsalicylate (up to 100 mg/day). The particular preparation studied produced a total serum salicylate concentration bioequivalent to only 50 mg acetylsalicylate.