Acupuncture & Herbal Clinic

Willow bark extract STW 33-I in the long-term treatment of outpatients with rheumatic pain mainly osteoarthritis or back pain. 

Four hundred and thirty-six patients with rheumatic pain mainly due to osteoarthritis (56.2%) and back pain (59.9%) used willow bark extract STW 33-I.  Pain reductions of 33% to 45% were seen over the course of the study (24weeks/6months).  http://www.ncbi.nlm.nih.gov/pubmed/23731658

Comment by TWACH:  Even though the dosage was not mentioned in this study, most research indicates daily dosage of 120 to 240 mg salicin should be used.