However, Martina Amanzio et al. (2001) demonstrated that "at least part of the physiological basis for the placebo effect is opiod in nature" (Bausell 2007: 160). We can be conditioned to release such chemical substances as endorphins, catecholamines, cortisol, and adrenaline. One reason, therefore, that people report pain relief from both acupuncture and sham acupuncture is that both are placebos that stimulate the opiod system.
In any case, there are difficulties that face any study of pain. Not only is pain measurement entirely subjective, but traditional acupuncturists evaluate success of treatment almost entirely subjectively, relying on their own observations and reports from patients, rather than objective laboratory tests. Furthermore, many individuals who swear by acupuncture (or therapeutic touch, reiki, iridology, meditation, mineral supplements, etc.) often make several changes in their lives at once, thereby making it difficult to isolate significant causal factors in a control group study.
Despite these difficulties, researchers can use the Von Korff Chronic Pain Grade Scale questionnaire and the back-specific Hanover Functional Ability Questionnaire (for back pain studies) to measure changes in back pain after various kinds of treatment. For example, a randomized, blinded study involving over 1,100 subjects with chronic back pain were given different treatments and evaluated after six months using both the Von Korff and the Hanover instruments. The study compared treatment by (1) acupuncture using traditional acupuncture points and methods, (2) acupuncture that used non-traditional points and methods (the needles weren't inserted as deeply or twirled as in traditional acupuncture, and (3) treatment involving drugs, exercise, and physical therapy. About twice as many in the groups stuck with needles responded to the treatment as in the non-needle group. It did not matter whether they were stuck in traditional points using traditional methods or in non-standard points using non-traditional methods. About 45% responded in these groups compared to about 25% in the group treated with drugs, exercise, and physical therapy. According to the BBC:
The researchers, from the Ruhr University Bochum, say their findings suggest that the body may react positively to any thin needle prick - or that acupuncture may simply trigger a placebo effect.