A curl of silver-grey willow bark showing its tan inner face, with a leaf. ← The FormularyLong game

White willow bark

Also known as Salix alba · salicis cortex · the bark salicin was first isolated from
CEVIDENCE

Where the aspirin story starts. The cautions came with it.

The honest take
Three honest things, and the third matters most. First, the good evidence for willow bark is not about joints. Cochrane rated it moderate for low back pain at 120–240 mg of salicin a day. In knee and hip osteoarthritis the trials disagree with each other: Schmid's 78-patient study at 240 mg salicin found a small benefit that scraped past significance (p = 0.047), and Biegert's 127-patient confirmatory trial at the same dose found nothing, while diclofenac in the same study separated from placebo cleanly. A 2023 meta-analysis pooled six arthritis trials and 329 patients, found a small effect on pain, and rated its own certainty of evidence very low. Second, our 150 mg is extract, not salicin. At 15% — the standardisation the EU monograph works from — that is roughly 22 mg of salicin a day: about a tenth of the trial dose, and less than half of the lowest daily dose that monograph permits. Third, the part that does not scale down. A dose too small to have been shown to do anything is not automatically too small to interact, because salicylate is still salicylate. It is here for completeness in a traditional joint stack, and that is what I would tell a friend. Then I would tell him, louder, that if aspirin is off the table for him, so is this.
What it is
The inner bark of the white willow, Salix alba, and its close relatives, extracted and standardised for salicin — the glycoside chemists isolated from willow in the 1820s and worked on until the chemistry ended in acetylsalicylic acid.
How it works
Salicin itself does very little. Gut bacteria and the liver convert it to saligenin and then to salicylic acid — the same end metabolite aspirin leaves behind — which damps prostaglandin production. Willow's polyphenols and flavonoids appear to contribute as well, which is why the whole extract does not behave exactly like the drug. The EU monograph carries the clearest numbers: 1,360 mg of quantified extract, equivalent to 240 mg of salicin, produced salicylic acid exposure equal to that expected from 87 mg of aspirin, peaking at about 1.2 mg/l two hours in. Unlike aspirin, willow bark does not shut platelets down irreversibly, but arachidonic-acid- and ADP-induced platelet aggregation still fell in patients taking it. Less than aspirin is not the same as none, and the interaction list follows the metabolite, not the marketing.
What it does
A traditional botanical used to support normal joint comfort and mobility.
Who it's for
Men with no salicylate problem who want the traditional bark in a joint stack and understand it is a small dose. Explicitly not for: anyone allergic or sensitive to aspirin, salicylates or NSAIDs, anyone taking warfarin, a DOAC or regular NSAIDs, anyone with severe liver or kidney disease, a peptic ulcer, a coagulation disorder, G6PD deficiency or salicylate-sensitive asthma, anyone pregnant or breastfeeding, anyone under 18, and anyone with surgery coming up.
How to use it
Two capsules daily with food, as part of the formula. Do not stack it on top of aspirin or an NSAID on the same day without medical advice — that is salicylate on salicylate. Tell any prescriber, dentist or surgeon that you take it. Stop if you get stomach pain, ringing in the ears, a rash, wheeze or unusual bruising, and do not restart without asking someone qualified. Worth knowing: the EU monograph caps medicinal willow bark use at four weeks, and nobody has studied daily use at this dose over years.
What to expect
At this dose, realistically nothing you will notice — which is the honest answer rather than a modest one. The trials that measured a change used six to ten times more salicin, ran four to six weeks, and still described the result as a modest improvement in reported pain. If a 150 mg bark extract produces a strong effect in you, treat that with suspicion rather than gratitude.
The research
Cochrane's herbal medicine for low back pain review (Gagnier et al., CD004504) found moderate evidence that Salix alba standardised to 120 mg or 240 mg of salicin daily beat placebo for short-term pain and rescue medication use, with one trial showing rough equivalence to 12.5 mg a day of rofecoxib — a drug withdrawn from the market in 2004. Chrubasik's 2000 trial in the American Journal of Medicine randomised 210 patients with exacerbations of chronic low back pain to 120 mg salicin, 240 mg salicin or placebo over four weeks and found a dose-dependent effect favouring 240 mg. The joint evidence is weaker and contradictory. Schmid's 2001 trial in Phytotherapy Research (78 patients, two weeks, 240 mg salicin a day) reduced WOMAC pain by 14% from baseline against a 2% rise on placebo, a difference of 6.5 mm (95% CI 0.2 to 12.7, p = 0.047). Biegert's two 2004 trials in the Journal of Rheumatology found no effect: in 127 outpatients with hip or knee osteoarthritis, WOMAC pain fell 8 mm (17%) on willow bark versus 5 mm (10%) on placebo, while diclofenac at 100 mg a day fell 23 mm (47%); a second trial in 26 patients with rheumatoid arthritis was negative and underpowered. Vlachojannis's 2009 systematic review in Phytotherapy Research concluded moderate evidence in low back pain and conflicting results in osteoarthritis, with all trials using up to 240 mg salicin a day for up to six weeks. A 2023 meta-analysis in Life (five studies, six RCTs, 329 arthritis patients) found a small pooled pain benefit (SMD −0.31, 95% CI −0.53 to −0.08, p = 0.007) and rated its own certainty of evidence very low; two of the pooled trials used 240 mg of salicin, while others used lower-strength proprietary preparations, including one at 150 mg of a 15% salicin extract, and the authors noted that other ingredients in multi-ingredient products may have contributed. Cochrane's 2014 osteoarthritis herbal review covered 33 interventions including a willow bark preparation; the moderate-quality osteoarthritis result in that review belongs to Boswellia serrata, not to willow. The EU herbal monograph (EMA/HMPC/80630/2016) sets the posology, caps well-established medicinal use at four weeks, contraindicates salicylate and NSAID hypersensitivity, salicylate-induced asthma, active peptic ulcer, severe hepatic or renal dysfunction, coagulation disorders, G6PD deficiency, the third trimester of pregnancy and use under 18, and states that willow bark may increase the effects of coumarin anticoagulants. Memorial Sloan Kettering additionally records anaphylaxis in an aspirin-allergic patient and fatal liver failure in a 28-month-old given paracetamol with willow bark tea. Not supported: weight loss, which Memorial Sloan Kettering lists as a purported use with no evidence behind it, and any claim that willow bark treats a joint disease.

Read the labelThis carries aspirin's cautions, not a gentle herb's. Do not take it if you are allergic or sensitive to aspirin, salicylates or NSAIDs, or if you have salicylate-sensitive asthma, an active peptic ulcer, severe liver or kidney disease, or a clotting disorder. Not for anyone under 18 — the same Reye's syndrome reason aspirin is not given to children. Speak to a doctor first if you take anticoagulants or methotrexate. Not for use in pregnancy. Not a treatment for arthritis or any joint condition.

Evidence grades describe how well an ingredient is studied — A well-supported, C emerging — not a promise of results. Educational, not medical advice. Doses are typical ranges; follow the label on the product.