From the Faculty of Social and Behavioural Sciences (Meeuwis, van Middendorp, Veldhuijzen, Evers), Institute of Psychology, Health, Medical and Neuropsychology Unit, Leiden University; and Leiden Institute for Brain and Cognition (Meeuwis, van Middendorp, Veldhuijzen, Evers), Departments of Dermatology (Lavrijsen) and Psychiatry (Evers), Leiden University Medical Center, Leiden, the Netherlands.
Psychosom Med. 2021 Jan 1;83(1):33-42. doi: 10.1097/PSY.0000000000000862.
Placebo effects may occur when it is known that an inert substance is given (i.e., open-label placebo). It is not yet clear whether these effects are similar to concealed (i.e., closed-label) placebo effects for itch or whether nocebo effects can be induced under open-label conditions.
Healthy volunteers (n = 112) were randomized to an open-label (I) or closed-label (II) positive suggestions group, or an open-label (III) or closed-label (IV) negative suggestions group. Participants were told, as cover story, that a transdermal caffeine patch would be applied that positively influences cognitive abilities and, as a side effect, positively or negatively (depending on group allocation) influences itch. Participants in the open-label groups were given a rationale explaining placebo and nocebo effect mechanisms. Itch (the primary outcome) was induced at baseline and postsuggestions by histamine iontophoresis.
Analyses of variance revealed significantly lower itch in the positive compared with the negative suggestions groups for both open- and closed-label contexts (all, p ≤ .008, Cohen d ≥ 0.47). Self-rated skin response was less severe after positive versus negative suggestions (all, p ≤ .017, Cohen d ≥ 0.33), but no effects on physical skin response were found (all, p ≥ .23, Cohen d ≤ 0.30).
Itch can be reduced by positive compared with negative suggestions under both open- and closed-label conditions. These findings indicate that open-label suggestions may potentially be a tool to use placebo effects for self-reported outcomes in clinical practice, for example, by explaining the role of expectancy in treatment. It needs to be investigated further under which circumstances an open-label rationale may impact placebo and nocebo effects.Trial Registration:www.trialregister.nl; NTR7174.
当已知给予惰性物质时，可能会出现安慰剂效应（即开放标签安慰剂）。目前尚不清楚这些效应是否与瘙痒的隐蔽（即封闭标签）安慰剂效应相似，或者在开放标签条件下是否可以诱导出反安慰剂效应。
将 112 名健康志愿者随机分为开放标签（I）或封闭标签（II）阳性建议组，或开放标签（III）或封闭标签（IV）阴性建议组。参与者被告知，作为掩盖故事，将应用一种经皮咖啡因贴片，该贴片可积极影响认知能力，并作为副作用，积极或消极（取决于组分配）影响瘙痒。开放标签组的参与者接受了一个解释安慰剂和反安慰剂效应机制的基本原理。在基线和建议后，通过组胺离子电渗法诱发瘙痒。
方差分析显示，在开放和封闭标签环境下，阳性建议组的瘙痒明显低于阴性建议组（均为 p ≤.008，Cohen d ≥ 0.47）。与负面建议相比，正面建议后的自我评估皮肤反应更轻（均为 p ≤.017，Cohen d ≥ 0.33），但对物理皮肤反应没有影响（均为 p ≥.23，Cohen d ≤ 0.30）。
在开放和封闭标签条件下，与负面建议相比，阳性建议可降低瘙痒。这些发现表明，开放标签建议可能是在临床实践中使用安慰剂效应报告自我报告结果的一种工具，例如，通过解释期望在治疗中的作用。需要进一步研究在什么情况下开放标签的基本原理可能会影响安慰剂和反安慰剂效应。
