Background: The double blind, non-penetrating placebo needle is effective in masking patients who are not informed that they may receive a placebo needle. In this study, we aimed to examine whether such needles are effective in masking subjects who have been so informed.
Methods: One hundred and fourteen informed, consenting, healthy volunteers were recruited. An experienced acupuncturist applied one of the following needle pairs - penetrating/non-penetrating, non-penetrating/non-penetrating, penetrating/penetrating - randomly at bilateral TE5 points in subjects who were informed that they would receive either a non-penetrating or a penetrating needle. After the application of a pair of needles, the subjects reported for each arm on whether they identified the needle as non-penetrating or penetrating. The patients also rated skin penetration/penetration-like pain and the deep dull pain (de qi) associated with the needle application on a visual analogue scale (VAS). The chi squared goodness of fit test was used to determine the probability of the number of correctly and incorrectly identified needles. Statistical comparisons for VAS scores for skin penetration pain and de qi were made using Mann-Whitneys U test.
Results: Of the 114 non-penetrating needle applications, the subjects identified 64 incorrectly and 50 correctly, fitting a probability of 0.5 (chi2=1.72, P=0.19). Most interestingly, the subjects identified 36 (32%) of 114 penetrating needle applications incorrectly. Skin penetration/penetration-like pain and de qi scores did not differ significantly (P=0.87 and P=0.17, respectively) between the 114 non-penetrating and 114 penetrating needles.
Conclusion: The non-penetrating placebo needle was effective in masking fully informed subjects. When used together with the matched penetrating needle, it has potential for use in double blind (patient and practitioner blind) studies.