Placebo interventions for all clinical conditions
Editorial Group: Cochrane Consumers and Communication Group
Published Online: 20 JAN 2010
Assessed as up-to-date: 10 NOV 2009
Copyright © 2010 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
How to Cite
Hróbjartsson A, Gøtzsche PC. Placebo interventions for all clinical conditions. Cochrane Database of Systematic Reviews 2010, Issue 1. Art. No.: CD003974. DOI: 10.1002/14651858.CD003974.pub3.
- Publication Status: New search for studies and content updated (conclusions changed)
- Published Online: 20 JAN 2010
Placebo interventions are often claimed to substantially improve patient-reported and observer-reported outcomes in many clinical conditions, but most reports on effects of placebos are based on studies that have not randomised patients to placebo or no treatment. Two previous versions of this review from 2001 and 2004 found that placebo interventions in general did not have clinically important effects, but that there were possible beneficial effects on patient-reported outcomes, especially pain. Since then several relevant trials have been published.
Our primary aims were to assess the effect of placebo interventions in general across all clinical conditions, and to investigate the effects of placebo interventions on specific clinical conditions. Our secondary aims were to assess whether the effect of placebo treatments differed for patient-reported and observer-reported outcomes, and to explore other reasons for variations in effect.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library Issue 4, 2007), MEDLINE (1966 to March 2008), EMBASE (1980 to March 2008), PsycINFO (1887 to March 2008) and Biological Abstracts (1986 to March 2008). We contacted experts on placebo research, and read references in the included trials.
We included randomised placebo trials with a no-treatment control group investigating any health problem.
Data collection and analysis
Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information. Trials with binary data were summarised using relative risk (a value of less than 1 indicates a beneficial effect of placebo), and trials with continuous outcomes were summarised using standardised mean difference (a negative value indicates a beneficial effect of placebo).
Outcome data were available in 202 out of 234 included trials, investigating 60 clinical conditions. We regarded the risk of bias as low in only 16 trials (8%), five of which had binary outcomes.
In 44 studies with binary outcomes (6041 patients), there was moderate heterogeneity (P < 0.001; I
In 158 trials with continuous outcomes (10,525 patients), there was moderate heterogeneity (P < 0.001; I
Meta-regression analyses showed that larger effects of placebo interventions were associated with physical placebo interventions (e.g. sham acupuncture), patient-involved outcomes (patient-reported outcomes and observer-reported outcomes involving patient cooperation), small trials, and trials with the explicit purpose of studying placebo. Larger effects of placebo were also found in trials that did not inform patients about the possible placebo intervention.
We did not find that placebo interventions have important clinical effects in general. However, in certain settings placebo interventions can influence patient-reported outcomes, especially pain and nausea, though it is difficult to distinguish patient-reported effects of placebo from biased reporting. The effect on pain varied, even among trials with low risk of bias, from negligible to clinically important. Variations in the effect of placebo were partly explained by variations in how trials were conducted and how patients were informed.
Plain language summary
Placebo interventions for all clinical conditions
Placebo interventions are often claimed to substantially improve many clinical conditions. However, most reports on effects of placebos are based on unreliable studies that have not randomised patients to placebo or no treatment.
We studied the effect of placebo treatments by reviewing 202 trials comparing placebo treatment with no treatment covering 60 healthcare problems. In general, placebo treatments produced no major health benefits, although on average they had a modest effect on outcomes reported by patients, such as pain. However, the effect on pain varied from large to non-existent, even in well-conducted trials. Variations in the effect of placebo was partly explained by variations in how trials were conducted, the type of placebo used, and whether patients were informed that the trial involved placebo.
安慰劑 (placebo) 的使用經常被認為可以改善病患報告結果(patientreported outcomes)以及觀察者報告結果(observerreported outcomes)，但這種信念並非依據比較使用安慰劑與不使用任何治療的隨機臨床試驗而來。
我們搜索了Cochrane Central Register of Controlled Trials (CENTRAL) 資料庫(2002年Cochrane Library第4期)，1966年至2002年間MEDLINE資料庫，1980年至2002年間EMBASE資料庫，1986年至2002年Biological摘要，以及1887年至2002年的PsycLIT資料庫。我們聯繫研究安慰劑方面的專家，並參考所納入臨床試驗的相關文獻。
研究數據結果是從182個可利用的臨床試驗中，選出其中的156個，來研究46種臨床狀況。我們在38個以二元結果(binary outcomes)呈現的研究中(總共有4284位病人)，並沒有在統計上發現安慰劑整體的影響，相對危險性(relative risk 0.95 (95% confidence interval (CI) 95% 信賴區間0.89 到 1.01))。病患報告結果的整體的相對危險性(relative risk) 為0.95 (95% 信賴區間0.88 到 1.03) ，觀察者報告結果的相對危險性relative risk為0.91 (95% 信賴區間0.81 1.03) 。雖然出現異質性(heterogeneity)(P = 0.01)，但漏斗散佈圖是對稱的。雖然信賴區間是寬鬆的，但我們在3個臨床試驗中，一共調查研究了4種臨床症狀(疼痛、噁心、抽煙以及憂鬱)，發現在統計學上，安慰劑的介入並沒有任何顯著的意義。我們從118個持續追蹤的臨床試驗結果中(7453位病人)，發現了安慰劑治療的整體效果，標準化平均差 (SMD) 為 −0.24 (95% 信賴區間CI −0.31 to −0.17) 。在病患報告結果中的標準化平均差為 −0.30 (95% 信賴區間CI −0.38 to −0.21) ，在觀察者報告結果中SMD標準化平均差為 −0.10 (95% 信賴區間CI −0.20 to −0.01) ，不具統計學上顯著的意義。縱使在大型的臨床試驗中，仍出現異質性(heterogeneity)(P<0.001)以及出現變異性很大的漏斗散佈圖。安慰劑的介入在疼痛 (SMD −0.25 (95% CI −0.35 to −0.16)) 以及在恐懼症 (SMD −0.63 (95% CI −1.17 to −0.08)) 有明顯的影響，但仍有潛在的偏差風險(risk of bias)。安慰劑的介入在超過3個臨床試驗中發現，對於8個其他的臨床症狀(噁心、抽煙、憂鬱、體重過重、氣喘、高血壓、失眠以及焦慮)來說，雖然信賴區間(confidence intervals)較寬，但在統計學上並沒有顯著的影響。
此翻譯計畫由臺灣國家衛生研究院 (National Health Research Institutes, Taiwan) 統籌。