This review evaluated the magnitude of the placebo response of sham acupuncture in trials of acupuncture for nonspecific LBP, and assessed whether different types of sham acupuncture are associated with different responses. Four databases including PubMed, EMBASE, MEDLINE, and the Cochrane Library were searched through April 15, 2023, and randomized controlled trials (RCTs) were included if they randomized patients with LBP to receive acupuncture or sham acupuncture intervention. The main outcomes included the placebo response in pain intensity, back-specific function and quality of life. Placebo response was defined as the change in these outcome measures from baseline to the end of treatment. Random-effects models were used to synthesize the results, standardized mean differences (SMDs, Hedges’g) were applied to estimate the effect size.

A total of 18 RCTs with 3,321 patients were included. Sham acupuncture showed a noteworthy pooled placebo response in pain intensity in patients with LBP [SMD −1.43, 95% confidence interval (CI) −1.95 to −0.91, I2=89%]. A significant placebo response was also shown in back-specific functional status (SMD −0.49, 95% CI −0.70 to −0.29, I2=73%), but not in quality of life (SMD 0.34, 95% CI −0.20 to 0.88, I2=84%). Trials in which the sham acupuncture penetrated the skin or performed with regular needles had a significantly higher placebo response in pain intensity reduction, but other factors such as the location of sham acupuncture did not have a significant impact on the placebo response.

The authors concluded that sham acupuncture is associated with a large placebo response in pain intensity among patients with LBP. Researchers should also be aware that the types of sham acupuncture applied may potentially impact the evaluation of the efficacy of acupuncture. Nonetheless, considering the nature of placebo response, the effect of other contextual factors cannot be ruled out in this study.

As the authors stated in their conclusion: the effect of other contextual factors cannot be ruled out. I would go much further and say that the outcomes noted here are mostly due to effects other than placebo. Obvious candidates are:

  • regression towards the mean;
  • natural history of the condition;
  • success of patient blinding;
  • social desirability.

To define the placebo effect in acupuncture trials as the change in the outcome measures from baseline to the end of treatment – as the authors of the review do – is not just naive, it is plainly wrong. I would not be surprised, if different sham acupuncture treatments have different effects. To me this would be an expected, plausible finding. But such differences just cannot be estimated in the way the authors suggest. For that, we would need an RCT in which patients are randomized to be treated in the same setting with a range of different types of sham acupuncture. The results of such a study might be revealing but I doubt that many ethics committees would be happy to grant their approval for it.

In the absence of such data, the best we can do is to design trials such that the verum is tested against a credible placebo which, for patients, is indistinguishable from the verum, while demonstrating that blinding is successful.

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