Vase Lene, Petersen Gitte Laue, Riley Joseph L, Price Donald D
Department of Psychology, Aarhus University, Jens Chr. Skous vej 4, 8000 Aarhus C, Denmark.
Pain. 2009 Sep;145(1-2):36-44. doi: 10.1016/j.pain.2009.04.008. Epub 2009 Jun 25.
Recent meta-analyses find various magnitudes of placebo analgesia effects in placebo mechanism trials versus placebo control trials, which have led to debate. To further investigate the magnitude of placebo analgesia in placebo mechanism trials the databases "PubMed", "PsycINFO" and "Web of Science" (2002-2007) were searched with the term "placebo analgesia". Twenty-one articles including 24 studies fulfilled the selection criteria (concerning: mechanisms, control, placebo treatment, randomization and pain measures). The validity of studies was assessed by the authors and effect sizes were calculated via difference scores. The magnitude of placebo analgesia in placebo mechanism studies was large (d=1.00) and about five times larger than placebo analgesia effects in placebo control studies (d=0.15-0.27). Differences in magnitude between the two types of studies appear to result from different types of suggestions given for pain relief. The magnitude of placebo effects was larger in studies that used long-term pain stimuli >20s (d=0.96) as opposed to short-term stimuli (d=0.81) and the largest placebo effects were found in studies wherein hyperalgesia was present (d=1.88). These results replicate our previous finding that placebo analgesic effects are higher in mechanism studies than in placebo control studies. However, since magnitudes of placebo analgesic effects are highly variable it may be valuable to investigate the factors and mechanisms that contribute to this variability as well as differences in magnitudes across types of studies.
近期的荟萃分析发现在安慰剂机制试验与安慰剂对照试验中存在不同程度的安慰剂镇痛效果，这引发了争论。为了进一步探究安慰剂机制试验中安慰剂镇痛的程度，我们在“PubMed”“PsycINFO”和“科学网”数据库（2002 - 2007年）中用“安慰剂镇痛”一词进行了检索。21篇文章（包含24项研究）符合入选标准（涉及：机制、对照、安慰剂治疗、随机分组和疼痛测量）。作者评估了研究的有效性，并通过差异分数计算效应量。安慰剂机制研究中的安慰剂镇痛程度较大（d = 1.00），约为安慰剂对照研究中安慰剂镇痛效果（d = 0.15 - 0.27）的五倍。两种类型研究在程度上的差异似乎源于为缓解疼痛所给出的不同类型的暗示。与短期刺激（d = 0.81）相比，使用>20秒的长期疼痛刺激的研究中安慰剂效应程度更大（d = 0.96），并且在存在痛觉过敏的研究中发现了最大的安慰剂效应（d = 1.88）。这些结果重复了我们之前的发现，即安慰剂机制研究中的安慰剂镇痛效果高于安慰剂对照研究。然而，由于安慰剂镇痛效果的程度变化很大，研究导致这种变化的因素和机制以及不同类型研究在程度上的差异可能是有价值的。
