Clinically meaningful nocebo effect occurs in acupuncture treatment: a systematic review

To investigate the nocebo effect using randomized acupuncture trials that include sham and no-treatment groups.

Electronic databases were searched to retrieve eligible trials from their inception until June 2013. Risk differences were then calculated using the acupuncture and sham groups to determine the treatment effect and the sham and no-treatment groups to determine the nocebo effect.

In total, 58 eligible trials were analyzed. On the basis of the rate of patients with any adverse event in 31 trials reporting available data, the treatment effect was 0.012 (95% confidence interval [CI]: 0.003, 0.021), with a number needed to harm (NNH) of 83 (95% CI: 48, 333). The nocebo effect was 0.049 (95% CI: 0.012, 0.086), with an NNH of 20 (95% CI: 12, 83). By contrast, the rate of dropouts due to adverse events in 39 trials reporting available data showed no differences for both effects. In addition, nearly 70% of the trials reported zero dropouts in the sham and no-treatment groups.

Our findings suggest that (1) the nocebo effect of acupuncture is clinically meaningful and (2) the rate of patients with any adverse event may be a more appropriate indicator of the nocebo effect.