The bark of the stately white willow tree (Salix alba) has been used in China for centuries as a medicine because of its ability to relieve pain and lower fever. Early settlers to America found Native Americans gathering bark from indigenous willow trees for similar purposes.

The active ingredient in white willow is salicin, which the body converts into salicylic acid. The first aspirin (acetylsalicylic acid) was made from a different salicin-containing herb--meadowsweet--but works in essentially the same way. All aspirin is now chemically synthesized. It's not surprising, then, that white willow bark is often called "herbal aspirin."

Although white willow is the species of willow tree most commonly used for medicinal purposes, other salicin-rich species are employed as well, including crack willow (Salix fragilis), purple willow (Salix purpurea), and violet willow (Salix daphnoides). These all may be sold under the label of willow bark.

The salicylic acid in white willow bark lowers the body's levels of prostaglandins, hormonelike compounds that can cause aches, pain, and inflammation. While white willow bark takes longer to begin acting than aspirin, its effect may last longer. And, unlike aspirin, it doesn't cause stomach bleeding or other known adverse effects.

Specifically, white willow bark may help to:

Relieve acute and chronic pain, including headache, back and neck pain, muscle aches, and menstrual cramps. The effectiveness of white willow bark for easing these and other types of discomforts results from its power to lower prostaglandin levels.

Control arthritis discomforts. Some arthritis sufferers taking white willow bark have experienced reduced swelling and inflammation, and eventually increased mobility, in the back, knees, hips, and other joints.

White willow bark should not be taken with aspirin or NSAIDs (nonsteroidal anti-inflammatory drugs) such as ibuprofen and naproxen; in combination, the herb and these drugs increase the chance of side effects such as stomach bleeding.

White willow bark can safely be taken long-term at recommended doses.

Higher than commonly recommended doses of this herb can cause stomach upset, nausea, or tinnitus (ringing in the ears). If any of these reactions develop, stop taking the herb.

Avoid white willow bark, which can irritate the stomach, if you are sensitive to aspirin, or if you have an ulcer or other gastrointestinal disorder.

Don't take white willow bark (or aspirin) if you have tinnitus.

Consult your doctor before taking this herb if you are pregnant or breast-feeding.

As with aspirin products, never give white willow bark to children or teenagers under age 16 with symptoms of the cold, the flu, or chicken pox. Although white willow bark is unlikely to cause the rare but potentially fatal condition called Reye's syndrome in such cases--it is metabolized differently than aspirin--the similarity to aspirin is close enough to warrant caution.