Background: There is ongoing debate about the efficacy of placebos in the treatment of mental disorders. In randomized control trials (RCTs) about the treatment of generalized anxiety disorder, the administration of a psychological placebo or placement on a waiting list are the two most common control conditions. But there has never been a systematic comparison of the clinical effect of these different strategies.
Aim: Compare the change in symptom severity among individuals treated with cognitive behavioral therapy, provided a psychological placebo, or placed on a waiting list using data from RCTs on generalized anxiety disorder.
Methods: The following databases were searched for RCTs on generalized anxiety disorder: PubMed, PsycInfo, EMBASE, The Cochrane Library, CNKI, Chongqing VIP, Wanfang, Chinese Biological Medical Literature Database, and Taiwan Electronic Periodical Services. Studies were selected based on pre-defined inclusion and exclusion criteria and the quality of each included study - based on the risk of bias and the level of evidence - was formally assessed. Meta-analysis was conducted using RevMan5.3 and network meta-analyses comparing the three groups were conducted using R.
Results: Twelve studies with a combined sample size of 531 were included in the analysis. Compared to either control method (placebo or waiting list), cognitive behavioral therapy was more effective for generalized anxiety disorder. Provision of a psychological placebo was associated with a significantly greater reduction of symptoms than placement on a waiting list. Eight of the studies were classified as 'high risk of bias', and the overall level of evidence was classified as 'moderate', indicating that further research could change the overall results of the meta-analysis.
Conclusions: RCTs about the treatment of generalized anxiety disorders are generally of moderate quality; they indicate the superiority of CBT but the results cannot, as yet, be considered robust. There is evidence of a non-negligible treatment effect of psychological placebos used as control conditions in research studies. This effect should be considered when designing and interpreting the results of randomized controlled trials about the effectiveness of psychotherapeutic interventions.
背景: 安慰剂对精神障碍的治疗疗效一直颇为争议。在广泛性焦虑障碍治疗的随机对照研究中，心理治疗安慰剂对照或等待治疗对照是两种最常见的对照设置。但是，目前尚缺乏这两种不同的对照策略对临床疗效影响的系统评价。
目标: 通过广泛性焦虑障碍的随机对照研究数据，比较认知行为治疗与心理治疗安慰剂对照或与等待治疗对照时患者症状严重程度的变化。
方法: 在以下数据库中检索有关广泛性焦虑障碍的随机对照研究：PubMed、PsycInfo、EMBASE、Cochrane Library、中国知识资源总库、中国科技期刊数据库、万方数据检索系统、中国生物医学文献服务系统以及台湾电子期刊服务网数据库等。根据预先设定的纳入和排除标准筛选文献，根据研究的偏倚风险和证据质量水平对每项纳入的研究进行全面的方法学质量评价。采用RevMan 5.3软件进行Meta分析，使用R软件进行3组比较的网络meta分析。
结果: 共纳入12项研究，总计样本量531例。相较于任何一种对照的方法（安慰剂或等待治疗），认知行为治疗对广泛性焦虑障碍的疗效更好。用心理治疗安慰剂的方法能比等待治疗显著减轻症状。这些研究中有8项被为“高偏倚风险”，研究的总体证据水平处于“中等”，表明将来的研究可能会改变这一Meta分析的总体结果。
结论: 总体而言，广泛性焦虑障碍治疗的随机对照研究的研究质量中等。虽然这些研究表明认知行为治疗具有优势，但迄今为止这一结果还不稳健。在这些研究中，心理治疗安慰剂对照组的治疗效果不可忽略。在随机对照研究中，无论是研究设计时还是解释有关心理治疗干预效应的结果时都应充分考虑安慰剂效应。
Keywords: cognitive behavioral therapy; effectiveness; generalized anxiety disorder; meta-analysis; placebo effect; randomized control trial.