White Willow Bark (Salix alba): Uses, Evidence and Safety

Willow bark is related to aspirin, and regulators list aspirin allergy, aspirin-sensitive asthma and age under 18 as reasons not to use it. The European Union herbal monograph lists salicylate or NSAID hypersensitivity, salicylate-sensitive asthma, active peptic ulcer, severe liver or kidney dysfunction, clotting disorders, G6PD deficiency, the third trimester of pregnancy, and age under 18 (because of the risk of Reye's syndrome) as contraindications. [1] It also says willow bark may increase the effects of anticoagulants such as coumarin derivatives. [1] Ask the prescriber or pharmacist before combining it with blood thinners or NSAIDs, and see how interactions work.

Overview

Willow bark is the dried bark of willow trees (Salix). EMA says the common name covers various species, including S. purpurea, S. daphnoides and S. fragilis. [2] Its compound salicin is converted in the body to salicylic acid, which is structurally related to aspirin. EMA says the amount of salicylic acid produced is small and the medicine's effects may be due to other components. [2] Aspirin was derived from salicin. [3]

Scientific name and plant part

Salix alba L. (white willow), family Salicaceae, is an accepted name. [4] The part used is the bark. The EU monograph covers several Salix species, and the trials cited here used standardized bark extracts, so check which species a product contains. [1] [5]

Traditional use

This is tradition, not proof. Memorial Sloan Kettering says willow bark has been used for thousands of years in China and Europe as a remedy for fevers and pain. [3] The EU committee accepted willow bark preparations for minor joint pain, fever with the common cold and headache based on traditional use of at least 30 years. [2]

What research shows

Forms and why the form matters

EMA says willow bark medicines are usually herbal tea or solid or liquid forms taken by mouth. [2] The EU monograph treats the dry extract (well-established use for low back pain) differently from tea and other preparations (traditional use). [1] Memorial Sloan Kettering says willow bark should not substitute for aspirin because of variation in its potency. [3] A 2015 review adds that extracts are usually standardized to salicin but other salicylates, polyphenols and flavonoids may also play roles. [7]

Safety

• Side effects: EMA lists allergic reactions (rash, itching, asthma) and stomach and gut symptoms (nausea, vomiting, abdominal pain, diarrhea, heartburn); frequency not known. [2]
• Allergy: a 2015 review says the primary cause for concern may be allergic reactions in salicylate-sensitive people. [7] Memorial Sloan Kettering cites case reports of anaphylaxis in a woman with aspirin allergy and of acute respiratory distress after a willow bark supplement. [3]
• Children and teens: the NHS says Reye's syndrome has been linked to salicylates, particularly aspirin, in young people and children under 16. [8] EU regulators contraindicate willow bark under 18 for this reason. [1] Memorial Sloan Kettering advises against giving it to children. [3] See children and teens.
• Blood thinners, NSAIDs and bleeding: Memorial Sloan Kettering says salicin affects platelets, to a lesser extent than aspirin, and lists warfarin, other blood thinners and NSAIDs as concerns. [3] A 2000 review lists willow bark among products that may raise bleeding risk or add to warfarin's effects, mostly from lab or single-case data. [9]
• Before surgery: Memorial Sloan Kettering says willow bark should be discontinued before surgery or chemotherapy because of bleeding risk; confirm timing with the surgical team. [3] See supplements before surgery.
• Liver and kidney: the EU monograph contraindicates use with severe liver or kidney dysfunction. [1] Memorial Sloan Kettering cites a case report of fatal liver failure in a 28-month-old boy given a tea containing willow bark along with acetaminophen. [3]
• Pregnancy and breastfeeding: the monograph says use in the first and second trimesters and during lactation is not recommended, because salicylates cross the placenta and appear in breast milk; it is contraindicated in the third trimester. [1] See pregnancy and breastfeeding.
• Duration: EMA says not to take it longer than 4 weeks for back or joint pain without medical advice. [2]

Quality notes

Ask a pharmacist about standardization and species. See quality testing and certifications. The sources we read do not describe contamination findings specific to willow bark.

Official statements

EMA/HMPC (European Union, 2017): well-established use for short-term low back pain (dry extract); traditional use for minor joint pain, fever with colds and headache; adults only. [2] [1]

A clinician or pharmacist decides what is right for a particular person.