Aspirin is the most widely used medicine in the world. It is used for relieving pain, reducing inflammation and fever. Aspirin is derived by boiling the bark of the white willow tree. The main ingredient in the medicine made from willow bark is called Salicin. Some people use willow bark as an alternative to aspirin. Willow bark is also used in some products for aiding weight loss. Willow trees and shrubs grow all over the world, except for Australia and Antarctica. The acid in aspirin can be found in jasmine, beans, peas, clover and certain grasses.