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White willow bark

Two systematic reviews report short-term low back pain relief over placebo with extracts giving 120 to 240 mg salicin a day, and one open trial found it similar to rofecoxib. Osteoarthritis results conflict, and a small rheumatoid arthritis trial found no difference from placebo. It slowed platelet clumping far less than aspirin. Anaphylaxis was reported with aspirin allergy.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Not FDA-approved as a drug for any condition.
Also called
Salix alba, willow bark extract, Salicis cortex, salicin, Salix daphnoides, Assalix, STW 33-I
Taken for
back pain, low back pain, osteoarthritis, arthritis, rheumatoid arthritis, joint pain

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help1

Reported risks2

What people take it for, and what was found

Shown to help1

Moderate

Low back pain

Shown to lower short-term pain in adults with flare-ups of low back pain at 120 or 240 mg salicin a day, more at the higher dose.

The numbers and sources
Effect
A Cochrane review found that extracts standardized to 120 or 240 mg salicin a day probably lower short-term pain and rescue medication use more than placebo (2 trials, 261 participants, moderate quality) [1]. In one of those trials of 210 people with a flare-up, pain-free patients in the last week numbered 39% on 240 mg, 21% on 120 mg and 6% on placebo (p < 0.001) [2]. In an open trial of 228 people, 240 mg salicin a day and 12.5 mg rofecoxib did not differ in pain scores after 4 weeks, with about 60% in each group responding [3]. A second systematic review rated the evidence for low back pain as moderate [4].
Population
Adults with acute flare-ups of chronic low back pain [1][2][3][4].
Sources
[1], [2], [3], [4]
Caveats
The rofecoxib trial was open label and graded very low quality [1][3]. Treatment lasted up to 6 weeks [4].

Mixed results1

Moderate

Osteoarthritis

Mixed results: a meta-analysis found more pain relief than placebo in osteoarthritis, while one trial found no difference from placebo, unlike diclofenac.

The numbers and sources
Effect
A 2023 meta-analysis of 6 RCTs (329 patients with arthritis) found more pain relief and better physical function than placebo [5]. In a 6-week trial of 127 people with hip or knee osteoarthritis, WOMAC pain fell 8 mm on 240 mg salicin a day, 23 mm on diclofenac and 5 mm on placebo. Willow bark did not differ from placebo (-2.8 mm, 95% CI -12.1 to 6.4, p 0.55), while diclofenac did (p 0.0002) [6]. A systematic review found conflicting results across osteoarthritis trials [4].
Population
Outpatients with hip or knee osteoarthritis [4][5][6].
Sources
[4], [5], [6]
Caveats
The meta-analysis authors judged the certainty of evidence inadequate because of potential bias [5].

Not shown to help1

Limited

Rheumatoid arthritis

One small trial found pain did not differ from placebo over 6 weeks in people with active rheumatoid arthritis.

The numbers and sources
Effect
In 26 people with active rheumatoid arthritis, pain fell 8 mm on 240 mg salicin a day and 2 mm on placebo over 6 weeks. The difference was not significant (-0.8 mm, 95% CI -20.9 to 19.3, p 0.93) [6].
Population
26 outpatients with active rheumatoid arthritis [6].
Sources
[6]
Caveats
A systematic review described this trial as grossly underpowered [4].

Doses studied

Trials used ethanol extracts giving 120 or 240 mg salicin a day for up to 6 weeks [2][4][6]. The rofecoxib comparison used 240 mg salicin a day for 4 weeks [3].

Risks

Reported risks2

Limited

Platelets and bleeding

One small trial found willow bark lowered platelet clumping slightly, far less than aspirin. Bleeding was not measured.

The numbers and sources
Effect
In people with low back pain, 240 mg salicin a day lowered maximal arachidonic acid-induced platelet aggregation to 61% against 78% on placebo (p 0.04). In heart patients on 100 mg aspirin a day it was 13%, a much stronger effect (p 0.001) [7]. The Cochrane review describes the willow bark effect on platelets as minimal next to a heart-protective aspirin dose [1].
Population
35 people with low back pain randomized to extract or placebo, and 16 heart patients on aspirin [7].
Sources
[1], [7]
Caveats
The trial measured platelet function in the lab, not bleeding events. Its authors state the relevance for people with impaired platelet function is unclear [7].
Limited

Allergy and anaphylaxis

Case reports: a woman with aspirin allergy had anaphylaxis after a supplement containing willow bark, and one trial participant had a severe allergic reaction.

The numbers and sources
Effect
A 25-year-old woman with a history of aspirin allergy had anaphylaxis needing epinephrine after 2 capsules of a weight loss supplement containing willow bark. The authors rated the supplement a probable cause [8]. In the 210-person back pain trial, one patient had a severe allergic reaction, perhaps to the extract [2].
Population
One case report [8] and one trial participant [2].
Sources
[2], [8]
Caveats
The case product contained other active ingredients besides willow bark [8].

Checked, no increase found1

Moderate

Adverse events in trials

Adverse events were about as common as on placebo in trials of up to 6 weeks in back pain and arthritis.

The numbers and sources
Effect
Across 6 RCTs in arthritis, the risk of any adverse event did not differ significantly from placebo [5]. The Cochrane back pain review noted no significant adverse events in its trials [1]. Adverse events were similar with willow bark and rofecoxib [3], and a systematic review reported minor adverse events [4].
Population
Trial participants with back pain and arthritis [1][3][4][5].
Sources
[1], [3], [4], [5]
Caveats
Trials lasted up to 6 weeks [4].

Claims tested and not found

  1. That willow bark eases osteoarthritis pain more than placebo. WOMAC pain did not differ from placebo over 6 weeks in 127 people, while diclofenac did [6].
  2. That willow bark eases rheumatoid arthritis pain. Pain did not differ from placebo in 26 people over 6 weeks [6].

Sources

  1. Oltean H, Robbins C, van Tulder MW, et al. Herbal medicine for low-back pain. Cochrane Database of Systematic Reviews. 2014. https://doi.org/10.1002/14651858.CD004504.pub4
  2. Chrubasik S, Eisenberg E, Balan E, et al. Treatment of low back pain exacerbations with willow bark extract: a randomized double-blind study. The American Journal of Medicine. 2000. https://doi.org/10.1016/S0002-9343(00)00442-3
  3. Chrubasik S, Künzel O, Model A, et al. Treatment of low back pain with a herbal or synthetic anti-rheumatic: a randomized controlled study. Willow bark extract for low back pain. Rheumatology. 2001. https://doi.org/10.1093/rheumatology/40.12.1388
  4. Vlachojannis JE, Cameron M, Chrubasik S. A systematic review on the effectiveness of willow bark for musculoskeletal pain. Phytotherapy Research. 2009. https://doi.org/10.1002/ptr.2747
  5. Lin CR, Tsai SHL, Wang C, et al. Willow Bark (Salix spp.) Used for Pain Relief in Arthritis: A Meta-Analysis of Randomized Controlled Trials. Life. 2023. https://doi.org/10.3390/life13102058
  6. Biegert C, Wagner I, Lüdtke R, et al. Efficacy and safety of willow bark extract in the treatment of osteoarthritis and rheumatoid arthritis: results of 2 randomized double-blind controlled trials. The Journal of Rheumatology. 2004. https://pubmed.ncbi.nlm.nih.gov/15517622/
  7. Krivoy N, Pavlotzky E, Chrubasik S, et al. Effect of salicis cortex extract on human platelet aggregation. Planta Medica. 2001. https://doi.org/10.1055/s-2001-12000
  8. Boullata JI, McDonnell PJ, Oliva CD. Anaphylactic reaction to a dietary supplement containing willow bark. Annals of Pharmacotherapy. 2003. https://doi.org/10.1345/aph.1D027

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