The term ‘placebo’ in acupuncture research is more complex than in pharmacological studies. Various forms of sham acupuncture have served as placebo controls [1], however, few of them may be acknowledged as genuine placebos as in the drug trials and are often misinterpreted [2].

The article recently published in Brain and Behavior, “Central correlates of placebo effects in nausea differ between men and women” has interesting findings related to placebo effect [3]. In this study, 90 healthy participants were randomly allocated into two different ‘placebo’ groups (30 participants to sham transcutaneous electrical nerve stimulation (TENS) at non-acupuncture points with low intensity or 30 to no electrical stimulation) or no treatment group (n = 30) and the authors assessed sex difference in the placebo effect on experimentally induced nausea. The authors found that women and men in the placebo group with improved nausea showed different activation patterns of electroencephalography, concluding that there could be sex difference in the mechanism of placebo effect. However, we would like to raise concerns regarding the use of the term “sham acupuncture” and the authors’ view on placebo presented in their study.

First, we argue that in the abstract, the term “sham acupuncture” was used inappropriately. Sham acupuncture can be defined as sham acupuncture techniques or devices used as control interventions in acupuncture studies [1,4]. It varies in the details of practice but can be broadly divided into two types: minimal insertion of the acupuncture needle (shallow needling) or no insertion with the sham acupuncture device (Table 1) [5].

Table 1

Type of sham acupuncture.

Types	Explanation	Appropriate usage	Included types
Minimal insertion	Acupuncture needles are inserted at non-acupuncture points or acupuncture points known to be unrelated to treatment. The depth of insertion is shallower than that of conventional acupuncture, and generally only minimal stimulation is applied. Manipulative techniques for inducing deqi are not common. It is performed using commonly used acupuncture needles.	It is appropriate for studies evaluating the effect of acupuncture according to the acupuncture points or depth, and the effect according to the intensity of stimulation.	Shallow needling and non-acupuncture point needling.
No insertion	Using sham acupuncture device, needles are not penetrated into the skin. Instead, a base unit that helps sham device to be attached to the skin is used in general so that the device can be retained on the skin. It can stimulate the same acupuncture points as the acupuncture does.	When assessing the effect of skin insertion is the main research question, sham device can be an appropriate control intervention for acupuncture studies.	Park sham needle, Streitberger needle, and Takakura needle.

Regardless of these differences, the main common characteristics of sham acupuncture are that it should resemble verum acupuncture in appearance, which is necessary for successful blinding, and that it should be physiologically inert, which is necessary for evaluating the specific effect of verum acupuncture. In their study, the authors used TENS on non-acupuncture points with no or low stimulation intensity. There is no description in the method section, but an additional verbal cue may have been given to participants to indicate potential efficacy. From a general perspective, the intervention in this study does not meet the criteria described above to be considered as “sham acupuncture” because TENS does not have any insertion or attachment of needle-like interventions on the body skin. Since the two interventions have markedly different application methods, it is not appropriate to use them interchangeably as a placebo control [6]. Apart from the fact that blinding is not possible for verum acupuncture, the mechanism of the placebo effect expected in this study may not be comparable to that of other types of sham acupuncture. Instead of the term “sham acupuncture”, a careful choice of an appropriate term for describing interventions should have been used. Second, we would like to point out a problem with the widespread perception of sham acupuncture as a placebo intervention. Placebos are mainly used in clinical drug trials to evaluate the specific effect of the test drug. The placebo effect can be defined as a nonspecific effect produced by participation in the study and ingestion of the placebo drug. In this context, various types of sham acupuncture have also been developed and used in clinical trials. However, we have already pointed out that sham acupuncture may have a unique physiological mechanism of action, so it may be inappropriate to use sham acupuncture to exclude specific effects in clinical acupuncture trials [1,4,7]. To assess the placebo effect, it would have been more appropriate to use a placebo pill commonly used in a drug trial. If sham acupuncture is used to evaluate the placebo effect, the intrinsic effect of sham acupuncture would be evaluated, which would lead researchers to unexpected results. Finally, there is one more issue regarding the real acupuncture in the acupuncture clinical trials. Acupuncture regimen in the clinical trials is quite different from those in the real-world practice. Real acupuncture in the sham device controlled studies might be different from the real acupuncture in the clinical practice because of additional device usage for mimicking sham device control [8]. From our previous network meta-analysis of different types of sham acupuncture studies, we have demonstrated that the effect size of real acupuncture in studies using sham device control group and those in studies using shallow needling control group is different which might be introduced by the different real acupuncture techniques [5]. The consequences of these issues are clear. In acupuncture studies using sham acupuncture, there is possibility for misinterpreting the effect of real acupuncture to the extent expected in actual clinical practice. It is inappropriate to use the sham acupuncture as the control treatment meaning the placebo treatment, in acupuncture research. It is time to reconsider the mistaken use of placebo mixed with sham acupuncture.

The authors declare no conflict of interest.