Salix spp., including Salix alba L., Salix purpurea L., Salix daphnoides Vill. and Salix fragilis L. · herb
Evidence tier: moderate
Relieves musculoskeletal pain and lower back pain
Not settled, and the obvious explanation fails on the numbers. Salicin is a prodrug: gut flora and the liver convert it to saligenin and then to salicylic acid, the same active metabolite aspirin produces, which inhibits COX enzymes and cuts prostaglandin synthesis. That is the textbook story and it is the reason for every safety warning. But the EMA assessment report says plainly that the serum salicylate levels produced by the RECOMMENDED doses of willow bark are TOO LOW to explain the analgesic activity, and suggests other constituents such as flavonoids or the salicin esters contribute. In cell work the whole extract inhibited COX-2 mediated PGE2 release and cut TNF alpha, IL-1 beta and IL-6, while salicin and salicylate alone did nothing. So the salicylate route explains the RISK but does not fully explain the BENEFIT.
Moderate, for ONE thing: short term low back pain. This is one of the rare herbs that clears a real regulatory efficacy bar. The EMA HMPC grants willow bark dry extract WELL ESTABLISHED USE status, meaning the efficacy is accepted on evidence rather than on tradition, for the short term treatment of low back pain. The 2014 Cochrane review of herbal medicine for low back pain agrees and is the source of the number: willow bark standardised to 120 mg or 240 mg salicin daily is probably better than placebo for short term improvement in pain and rescue medication use, rated MODERATE quality evidence, but that rests on just two trials in 261 people, and it was tested only short term (up to six weeks). A third trial (228 people) found 240 mg salicin comparable to 12.5 mg rofecoxib, but Cochrane rated that very low quality and rofecoxib has since been withdrawn from the market. Everything beyond low back pain drops away. Osteoarthritis is NOT supported: the EMA assessment report states that in osteoarthritis patients the borderline significant effect could not be confirmed in a later clinical study, and NCCIH notes a 2019 review that recommends AGAINST willow bark for chronic musculoskeletal pain. The EMA's other indications (minor joint pain, fever with a cold, headache) are TRADITIONAL USE only, based exclusively on long standing use, not on trials. The decisive fact about this ingredient is not its efficacy, it is its identity: willow bark is the botanical precursor of aspirin, and it inherits aspirin's contraindications wholesale. EMA contraindicates it in hypersensitivity to salicylates or other NSAIDs, asthma due to salicylate sensitivity, active peptic ulcer disease, coagulation disorders, G6PD deficiency, severe liver or renal dysfunction, the third trimester of pregnancy, and in ALL children and adolescents under 18 because of the risk of Reye's syndrome.
EMA well established use, the only dose with efficacy evidence behind it: dry extract (8 to 14:1, ethanol 70 percent, standardised to 15 percent total salicin), single dose 393 mg to 786 mg up to twice daily, daily dose 393 mg to 1,572 mg, taken after meals with plenty of hot water. That works out to roughly 120 mg to 240 mg total salicin daily, which is the dose range Cochrane tested. Not to be used for more than 4 weeks. Contraindicated under 18 years of age. Traditional preparations are dosed differently (dry aqueous extract 600 mg twice daily, or 1 to 3 g comminuted bark as a tea three times daily).
Onset slower than aspirin, allow 1 to 2 hours for full effect. Maximum 4 week continuous use without medical review.
Avoid in pregnancy (contains salicylates, aspirin like risk of premature closure of ductus arteriosus in third trimester; bleeding risk in first trimester). Avoid in breastfeeding. Contraindicated in aspirin hypersensitivity, active peptic ulcer, and renal impairment. Caution with anticoagulants.
Pregnancy: avoid
Breastfeeding: avoid
Active compounds: salicin, salicortin, 2'-O-acetylsalicortin, tremulacin, flavonoids, condensed tannins, catechins
Remedies using Willow Bark · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.