To assess the clinical efficacy of a chemically standardized willow bark extract in the treatment of osteoarthritis.
Willow bark extract, in a dose corresponding to 240 mg salicin/day, was compared to placebo in a 2-week, double-blind, randomized controlled trial. The primary outcome measure was the pain dimension of the WOMAC Osteoarthritis Index. Secondary outcome measures included the stiffness and physical function dimensions of the WOMAC, daily visual analogue scales (VAS) on pain and physical function, and final overall assessment by both patients and investigators.
78 patients (39 willow bark extract, 39 placebo) participated in the trial. A statistically significant difference between active treatment and placebo group was observed in the WOMAC pain dimension (d = 6.5 mm, 95% C.I. = 0.2-12.7 mm, p = 0.047); the WOMAC pain score was reduced by 14% from baseline level after two weeks of active treatment, compared to an increase of 2% in the placebo group. Patient diary VAS confirmed this result, and likewise the final overall assessments showed superiority of willow bark extract over placebo (patients assessment, p = 0.0002; investigators assessment, p = 0.0073).
Willow bark extract shows a moderate analgesic effect in osteoarthritis.