Placebo Response among Different Types of Sham Acupuncture for Low Back Pain: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Background: Low back pain (LBP) is a prevalent and debilitating condition that poses a significant burden on healthcare systems. Acupuncture has been proposed as a promising intervention for LBP, but the evidence supporting its specific effect is insufficient, and the use of sham acupuncture as a control in clinical trials presents challenges due to variations in sham acupuncture techniques and the magnitude of the placebo effect.

Objective: To investigate the magnitude of the placebo response of sham acupuncture in trials of acupuncture for nonspecific LBP, and to assess whether different types of sham acupuncture are associated with different responses.

Methods: 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.

Results: 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, I=89%]. A significant placebo response was also shown in back-specific functional status (SMD -0.49, 95% CI -0.70 to -0.29, I=73%), but not in quality of life (SMD 0.34, 95% CI -0.20 to 0.88, I=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.

Conclusions: 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. (PROSPERO registration No. CRD42022304416).