Willow bark contains a chemical called salicin that is similar to aspirin.
Willow bark is the bark from several varieties of the willow tree, including white willow or European willow, black willow or pussy willow, crack willow, purple willow, and others. The bark is used to make medicine. Willow bark acts a lot like aspirin, so it is used for pain, including headache, muscle pain, menstrual cramps, rheumatoid arthritis (RA), osteoarthritis, gout, and a disease of the spine called ankylosing spondylitis. Willow bark’s pain relieving potential has been recognized throughout history. Willow bark was commonly used during the time of Hippocrates, when people were advised to chew on the bark to relieve pain and fever. Willow bark is also used for fever, the common cold, flu, and weight loss.