Bark extract from willow species, standardised to salicin — a compound the body converts to salicylic acid, the same metabolite produced by aspirin.
Willow bark is best understood as a slow, variable, unmeasured dose of a salicylate. The conversion of salicin to salicylic acid means it inherits aspirin’s risk profile — gastrointestinal bleeding, Reye syndrome in children, asthma exacerbation — without the dose precision. Trials in low back pain used standardised salicin content that ordinary bark preparations rarely state.
Sold as
Standardised bark extract, Capsule, Tea, Tincture
Standardised to
Trials use extract standardised to 120 or 240 mg salicin per day — a product without this marker may not resemble what was studied.
Also known as
Salix, Willow bark, Salicin extract
Regulation: Registered in parts of Europe as a traditional herbal medicine for minor joint and back pain. Because it is metabolised to salicylate, warnings that apply to aspirin — including avoidance in children with fever — apply here too.
What the research used
The amounts, forms and durations published trials of White willow bark actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Low back pain
120–240 mg
Limited
Standardised extract expressed as salicin, daily · 4 weeks
The 240 mg salicin arm outperformed 120 mg in the main trials. For comparison, this is a far smaller salicylate exposure than a standard aspirin dose, which is why it acts slowly and weakly.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🍽️With food
Not enough
Taken with food to reduce stomach irritation, following the same reasoning as with aspirin. Not compared in trials.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Not enough
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Some trials report reduced low back pain over four weeks with a standardised salicin extract, with a larger effect at the higher dose. The literature is small, mostly from one European group, and reviewers describe the evidence as insufficient to be confident.
What may be going on: Salicin is metabolised to salicylic acid, which inhibits cyclooxygenase enzymes — the same pathway aspirin acts on.
Not enough evidence. Not enough human research to say anything useful yet.
No source is attached to this association yet, so it is rated not enough evidenceby default. It is listed because people commonly ask about it — not because there is evidence for it.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Avoid
Aspirin allergy and salicylate sensitivity
Anyone who reacts to aspirin or non-steroidal anti-inflammatories, including people with aspirin-exacerbated respiratory disease, should avoid willow bark. It delivers the same active metabolite.
Avoid
Not for children with fever or viral illness
Salicylates are linked to Reye syndrome, a rare but often fatal condition affecting the liver and brain in children with viral infections. Willow bark should not be given to children or teenagers with a fever.
Interaction
Bleeding risk with anticoagulants and NSAIDs
Interacts withWarfarin, direct oral anticoagulants, aspirin, NSAIDs
Willow bark adds to the bleeding and gastrointestinal risk of warfarin, direct oral anticoagulants, aspirin and other non-steroidal anti-inflammatories, and should be stopped before surgery.
Worth knowing
Kidney and stomach effects
As a salicylate source it carries the same concerns as low-dose aspirin for gastric irritation and for kidney function in people with existing kidney disease or dehydration.
Avoid
Pregnancy, particularly the third trimester
Salicylates in late pregnancy are associated with effects on the fetal circulation and on bleeding at delivery. Willow bark is best avoided throughout pregnancy.