To investigate the efficacy and safety of a standardized willow bark extract in patients with osteoarthritis (OA) and rheumatoid arthritis (RA).
We studied 127 outpatients with hip or knee OA and a WOMAC pain score of at least 30 mm and 26 outpatients with active RA in 2 randomized, controlled, double-blind trials with followup for 6 weeks. OA trial: Patients were randomized to receive willow bark extract, corresponding to 240 mg of salicin/day, diclofenac 100 mg/day, or placebo (n = 43, 43, and 41, respectively). Main outcome measure was the pain subscore of the WOMAC OA Index. RA trial: Patients were randomized to receive willow bark extract, corresponding to 240 mg salicin/day (n = 13) or placebo (n = 13). Main outcome measure was the patient's assessment of pain rated on a 100 mm visual analog scale (VAS).
OA trial: WOMAC pain scores decreased by 8 mm (17%) in the willow bark group and by 23 mm (47%) in the diclofenac group, compared with 5 mm (10%) in the placebo group. The difference between willow bark extract and placebo was not statistically significant (-2.8 mm; 95% CI -12.1 to 6.4 mm; p = 0.55, ANCOVA), but the difference between diclofenac and placebo was highly significant (-18.0 mm; 95% CI -27.2 to -8.8 mm; p = 0.0002, ANCOVA). RA trial: The mean reduction of pain on the VAS was -8 mm (15%) in the willow bark group compared with -2 mm (4%) in the placebo group. The difference was not statistically significant (estimated difference -0.8 mm; 95% CI -20.9 to 19.3 mm; p = 0.93, ANCOVA).
The OA study suggested that the willow bark extract showed no relevant efficacy in patients with OA. Similarly, the RA trial did not indicate efficacy of this extract in patients with RA.