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Can willow bark be used to relieve pain?

BACKGROUND

Willow bark has been used to relieve pain, fevers and inflammatory problems since ancient times. It is mentioned in the medical records of ancient Egypt and the writings of the 5th-century BC Greek physician Hippocrates. In 1763, the first modern medical report of its effectiveness was published. Many willow species have been used medicinally, most commonly the European white willow (Salix alba) and the North American black willow (Salix nigra). The active ingredients are a group of compounds called salicylates.

The use of willow bark is closely tied to the development of the modern pharmaceutical industry. In 1829, a French pharmacist purified salicin from extracts of willow bark. Although inactive itself, once absorbed into the body, salicin is converted into salicylic acid, the active compound. Salicin and salicylic acid were widely used analgesics in the 19th century, but the

high doses (up to 10gm daily) routinely led to stomach irritation and vomiting.

Researchers at the German pharmaceutical company Bayer sought a compound that caused less irritation. They discovered acetylsalicylic acid, first marketed in 1899 as aspirin.

Although Felix Hoffman is often credited with this discovery, investigations stimulated by aspirin’s centenary have questioned this tradition. The evidence crediting Hoffman has always been weak, but papers recently uncovered in Bayer’s archives suggested that Arthur Eichengrün should have received the credit.

Several salicylates were made at Bayer, but none were thought to be useful. Only Eichengrün persisted with this line of research, and instructed Hoffman to make acetylsalicylic acid without telling him why. In the 1930s, when Hoffman was publicly credited with the discovery, Eichengrün was in no position to protest.

Although a successful and wealthy industrial chemist, he was Jewish and could not risk drawing attention to himself. Although he survived a Nazi concentration camp and published his account in 1949, it went practically unnoticed until aspirin’s centenary.

EVIDENCE FROM STUDIES

The gastrointestinal problems noted

in the 19th century, coupled with aspirin’s success, led to a neglect of willow bark. This has changed in recent years, with research identifying several ingredients with anti-inflammatory and pain-relieving properties. These act via additional mechanisms compared to salicin.

A systematic review identified six randomised controlled trials involving willow bark.

Patients with low back pain had significant relief compared to placebo and similar pain-relief compared to those given conventional over-the-counter analgesics.

However, patients with osteoarthritis did not experience benefits. In one study where blood clotting was examined, willow bark did not have a blood-thinning effect. Stomach problems were also found to be much less prevalent than expected compared to aspirin.

PROBLEMATIC ASPECTS

Willow bark can cause gastrointestinal problems. Some people are allergic to willow bark because of its salicylates. Anyone allergic to aspirin should not use willow bark preparations.

Large doses of salicin can damage the kidneys, leading in rare cases to what is called renal papillary necrosis. The first recorded instance of this condition was in the composer Ludwig von Beethoven. The large amounts of salicin which he ingested are believed to have contributed to his death.

RECOMMENDATIONS

Willow bark contains a number of ingredients that act as pain relievers. It appears to be most helpful for generalised pain, like low back pain. The evidence is less supportive for use with arthritic pain, but this may be because the studies used doses that were too low to be effective (up to 240mg salicin per day).

Willow bark has advantages over aspirin as it causes less gastrointestinal irritation.

Those taking aspirin for its blood-thinning effects should not use willow bark instead as willow does have these effects.

Although connected closely in history, willow bark and aspirin are very different in their effects.


Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University