The white willow is a deciduous tree native to Europe and introduced throughout temperate regions of North America. Growing up to 25 meters in height, white willow usually flowers in early spring, bearing small cylindrical catkins, with male and female flowers on separate trees. The tree has long, narrow, lanceolate leaves, covered with short hairs on both sides. The fruit consists of small capsules filled with light, downy seeds, which are readily transported via wind. White willow has a rough grayish bark, which is used for health purposes.
The principal constituent of white willow bark is a glycoside compound known as salicin.
The recommended dosage for white willow bark varies according to its salicin content. Commission E recommends a dosage corresponding to 60 to 120 mg of salicin per day. Although the herb has no known side effects at this dosage range, some individuals may experience allergic responses. Because it is closely related to aspirin, white willow bark is not recommended in cases where aspirin is contraindicated, such as people with ulcers or children with fevers.