Is acupuncture analgesia an expectancy effect? Preliminary evidence based on participants' perceived assignments in two placebo-controlled trials.

This purpose of this article is to contrast the analgesic efficacy of acupuncture following dental surgery with the analgesic effects based on the expectation of benefit in two independently conducted placebo-controlled trials evaluating acupuncture as an adjunctive therapy for dental surgery. Both trials used pain following dental surgery as the outcome variable, and both included a blinding check to ascertain patients' beliefs regarding which treatment they were receiving. Although no statistically significant analgesic effect was observed between the acupuncture and placebo groups, participants in both experiments who believed they received real acupuncture reported significantly less pain than patients who believed that they received a placebo. Patients' beliefs regarding the receipt of acupuncture bore a stronger relationship to pain than any specific action possessed by acupuncture. These results also support the importance of both employing credible controls for the placebo effect in clinical trials and evaluating the credibility of those controls.