Willow bark

What is it?

Willow bark is a herbal preparation that’s available over the counter in the form of tablets. Its active ingredient, salicin, reduces the production of pain-inducing chemicals in your nerves. Limited evidence suggests that willow bark may have a moderate effect in treating pain caused by osteoarthritis and rheumatoid arthritis. In the single study testing it against a non-steroidal anti-inflammatory drug (NSAID) for osteoarthritis, it wasn’t as effective for pain relief.

  • Family: Herbal medicine of the willow (Salicaceae) family
  • Scientific name: Willow
  • Other names: Salix spp., basket willow, bay willow, beta-salicin, black willow, brittle willow, crack willow, daphne willow, populin, purple willow, salicin, salicortin, salicoylsalicin, salicyl alcohol, salicylate, salicylic acid, salicyluric acid, salidroside, saligenin, salipurposide, Salix alba, Salix daphnoides, Salix fragilis L., Salix pentandra, Salix purpurea, white willow, white willow bark, willow tree, willowprin

The bark of some species of Salix trees has been used for treating inflammatory and arthritis-related conditions since ancient times. Extracts from the following species of Salix trees have been used as sources of willow:

  • Salix purpurea (purple willow)
  • Salix fragilis (crack willow)
  • Salix alba (white willow)
  • Salix daphnoides (violet willow)
  • Salix pentandra (bay willow).

These Salix species are also considered the natural source of acetylsalicylic acid, also known as aspirin. You can buy willow bark capsules from UK-based internet sites.

How does it work?

Willow bark contains an ingredient called salicin, which your body makes into another chemical substance called salicylic acid. Similar to acetylsalicylic, salicylic acid reduces the production of certain prostaglandins (hormone-like substances that control your immune system and fight joint inflammation) in your nerves, and this eases pain and discomfort. Willow bark showed anti-inflammatory activity in several laboratory-based studies.

Is it safe?

You should use willow bark with caution if you have gastrointestinal and liver problems or diabetes. Like aspirin, you should also be careful if you take anticoagulants, acetazolamide, anti-hypertensives and anti-inflammatory drugs because willow bark interacts with these drugs.

Common side-effects include:

  • stomach upsets
  • increased blood pressure
  • allergic reactions.

A daily dose of 240 mg of salicin has been used in previous studies on participants with osteoarthritis and rheumatoid arthritis. Assalix®, a commercial willow bark preparation, contains 240 mg of salicin per tablet. Overdose can lead to serious consequences, including stomach ulcers and bleeding.

Willow bark trials for rheumatoid arthritis

In this trial, 26 participants with rheumatoid arthritis were randomly given either willow bark (240 mg salicin) or placebo tablets once a day for six weeks. Participants taking willow bark had a 15% reduction in pain compared to a 4% reduction in the placebo group, but the study’s authors concluded that this difference may be due to chance.

Willow bark trials for osteoarthritis

Two RCTs were found examining the effectiveness of willow bark in treating hip and knee osteoarthritis. Willow bark was well-tolerated by participants who received it in both RCTs. Lack of effectiveness was the most common reason for withdrawal.

Trial 1

In the first trial, 127 participants were randomised to receive willow bark (240 mg of salicin), 100 mg diclofenac (a non-steroidal anti-inflammatory drug) or a placebo once a day for six weeks.

  • Participants who were on diclofenac had the best levels of pain relief.
  • Those assigned willow bark didn’t significantly differ from the placebo group.

Trial 2

In the second trial, 78 participants were randomly assigned to either willow bark (240 mg of salicin) or placebo tablets once a day for two weeks. Participants taking willow bark achieved a 14% reduction in pain, compared to only 2% in the placebo group.