Walach Harald, Schneider Rainer
School of Social Sciences, European Office of the Samueli Institute for Information Biology, University of Northampton, UK.
Hum Psychopharmacol. 2009 Oct;24(7):549-58. doi: 10.1002/hup.1054.
We employed the placebo-caffeine paradigm to test whether the presence or absence of a substance (caffeine) influences the placebo effect.
In experiment 1 consisting of four conditions with n = 15 participants each (control, placebo, two double-blind groups, each with placebo only), we maximized the placebo effect through expectation. Effects were assessed with physiological (blood pressure, heart rate), psychomotor (response times), and well-being indicators (self-report). In experiment 2, caffeine was administered in one of the double-blind groups, and another condition was added where caffeine was given openly.
Effect sizes were medium to large for some outcome parameters in experiment 1 and 2, showing partial replicability of the classical placebo effect. Although not formally significant, differences between the double blind placebo conditions of the two experiments (with and without caffeine present) were medium to small. There was a significant difference (p = 0.03) between experiment 1 and experiment 2 in the physiological variables, and a near significant interaction effect between groups and experiments in the physiological variables (p = 0.06).
The question warrants further scrutiny. The presence of a pharmacological substance might change the magnitude of the placebo response.
我们采用安慰剂 - 咖啡因范式来测试一种物质（咖啡因）的存在与否是否会影响安慰剂效应。
在实验1中，共有四个条件，每个条件有n = 15名参与者（对照组、安慰剂组、两个双盲组，每组仅使用安慰剂），我们通过期望最大化安慰剂效应。通过生理指标（血压、心率）、心理运动指标（反应时间）和幸福感指标（自我报告）来评估效果。在实验2中，在其中一个双盲组中给予咖啡因，并增加了另一个公开给予咖啡因的条件。
在实验1和实验2中，某些结果参数的效应大小为中等至较大，表明经典安慰剂效应具有部分可重复性。尽管未达到统计学显著性，但两个实验的双盲安慰剂条件（有无咖啡因）之间的差异为中等至较小。在生理变量方面，实验1和实验2之间存在显著差异（p = 0.03），并且在生理变量方面，组与实验之间存在接近显著的交互作用（p = 0.06）。
这个问题值得进一步研究。药理物质的存在可能会改变安慰剂反应的程度。
