Willow trees are the original natural source of salicin, the compound that helped inspire aspirin.
Willows belong to the genus Salix, which includes hundreds of species found across much of the Northern Hemisphere. Their bark contains salicylates, including salicin. After ingestion, salicin is converted through metabolic steps into salicylic acid, a compound with pain-relieving and fever-reducing properties.
People used willow bark medicinally long before modern chemistry. In the 19th century, chemists isolated and studied salicylic acid, but it could irritate the stomach. In 1897, Felix Hoffmann at Bayer produced a more suitable form of acetylsalicylic acid, which became widely known as aspirin.
Aspirin is not simply powdered willow bark: modern aspirin is manufactured as a defined chemical compound. Willow extracts and aspirin also differ in dose, purity, and safety. The tree’s name is connected with the scientific term salicylate through the Latin name Salix.