This hypthesis gives topical capsaicin some degree of logic - remove the neurotransmitter, so remove the pain. Zhang and Li Wan Po searched the literature for capsaicin papers using a sensitive strategy. They sought reports of clinical investigations. Each symbol represents the proportion of patients in each trial reaching some clinical end-point for benefit, and the number next to the symbol the number of patients treated with topical capsaicin. Capsaicin results are plotted against placebo results.
Points lying between the line of equality and the capsaicin axis are trials showing benefit.
This plot is a simple representation of how similar or dissimilar trial results were found to be. A total of 144 patients were treated with capsaicin and 165 with placebo cream. The end point was a physician global assessment of pain relief. For every four patients treated with topical capsaicin, one would have had the pain of diabetic neuropathy relived who would not have had they been treated with placebo. The end point was articular tenderness or physicians global assessment of pain relief.