Willow bark has been used as a treatment for pain and fever in China since 500 BC. In Europe, it was primarily used for altogether different purposes, such as stopping vomiting, removing warts, and suppressing sexual desire. However, in 1828, European chemists made a discovery that would bring together some of these different uses. They extracted the substance salicin from white willow, which was soon purified to salicylic acid. Salicylic acid is an effective treatment for pain and fever, but it is also sufficiently irritating to do a good job of burning off warts.

Chemists later modified salicylic acid (this time from the herb meadowsweet) to create acetylsalicylic acid, or aspirin.

As interest in natural medicine has grown, many people have begun to turn back to white willow as an alternative to aspirin. One double-blind, placebo-controlled trial found it effective for back pain, and another found it helpful for osteoarthritis. It is also used for such conditions asbursitis, dysmenorrhea, tension headaches, migraine headaches, rheumatoid arthritis, and tendonitis. However, two recent studies failed to find it effective for rheumatoid arthritis or osteoarthritis.

Aspirin and related anti-inflammatory drugs are notorious for irritating or damaging the stomach. However, when taken in typical doses, willow does not appear to produce this side effect to the same extent.1,2This may be partly due to the fact that most of the salicylic acid provided by white willow comes from salicin and other chemicals that are only converted to salicylic acid after absorption into the body.3Other evidence suggests that standard doses of willow bark are the equivalent of one baby aspirin daily rather than a full dose.4

This latter finding raises an interesting question: If willow provides only a small amount of salicylic acid, how can it work? The most likely answer seems to be that other constituents besides salicin play a role. Another possibility may be that the studies finding benefit were flawed, and that it actually does not work.