Evidence Behind the Placebo Effect
Many studies have been completed over the past few years surrounding placebos and the responses the have been seen in patients. Theses studies have looked at a wide range of clinical conditions including pain, Parkinson's Disease, multiple sclerosis and epilepsy. This section of the website will analyze the 2010 Cochrane Review which looked at that the placebo effect.
Many studies have been completed over the past few years surrounding placebos and the responses the have been seen in patients. Theses studies have looked at a wide range of clinical conditions including pain, Parkinson's Disease, multiple sclerosis and epilepsy. This section of the website will analyze the 2010 Cochrane Review which looked at that the placebo effect.
Placebo interventions for all clinical conditions
Objective
This 2010 Cochrane Review by Hrobjartsson and Gotzsche was completed "to assess the effect of placebo interventions across all clinical conditions, and to investigate the effects of placebo interventions on specific clinical conditions."
The authors also wished to determined if the response elicited by placebo varied based on whether the patient or the observer documented the outcomes.
Methods
The authors searched a variety of databases including:
Inclusion Criteria: "we included randomized placebo trials with a no-treatment control group investigating any health problem"
The trials were obtained and analyzed by the two authors mentioned above. The authors completed their assessments separately from one another and ensured that any extra information needed from the included trials was obtained. Trials were analyzed based on whether they had binary outcomes, in which case relative risk (RR) was used, or whether they had continuous outcomes, in which case standardized mean difference (SMD) was used.
Results
202 trials provided outcome data for this review and covered 60 medical conditions.
It should be noted that the authors determined that only 8% of trials had a low risk of bias associated with their results.
Out of the 44 trials with binary outcomes the authors found:
Out of the 158 trials with continuous outcomes the authors found:
Authors' Conclusions
"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."
Objective
This 2010 Cochrane Review by Hrobjartsson and Gotzsche was completed "to assess the effect of placebo interventions across all clinical conditions, and to investigate the effects of placebo interventions on specific clinical conditions."
The authors also wished to determined if the response elicited by placebo varied based on whether the patient or the observer documented the outcomes.
Methods
The authors searched a variety of databases including:
- Cochrane Central Register of Controlled Trials
- MEDLINE
- EMBASE
- PsychINFO
- Biological Abstracts
- Contacted experts
- Noted references in trials which were chosen in this review
Inclusion Criteria: "we included randomized placebo trials with a no-treatment control group investigating any health problem"
The trials were obtained and analyzed by the two authors mentioned above. The authors completed their assessments separately from one another and ensured that any extra information needed from the included trials was obtained. Trials were analyzed based on whether they had binary outcomes, in which case relative risk (RR) was used, or whether they had continuous outcomes, in which case standardized mean difference (SMD) was used.
Results
202 trials provided outcome data for this review and covered 60 medical conditions.
It should be noted that the authors determined that only 8% of trials had a low risk of bias associated with their results.
Out of the 44 trials with binary outcomes the authors found:
- moderate heterogeneity
- pooled effect of placebo = RR 0.93 (95%CI, 0.88 to 0.99)
- because the RR was less than 1 this indicated that the placebo had a positive effect
- no statistically significant effect of placebo for pain, nausea, smoking and depression (wide confidence interval)
Out of the 158 trials with continuous outcomes the authors found:
- moderate heterogeneity
- overall impact of placebo = SMD -0.23 (95%CI, -0.28 to -0.17)
- because the SMD was negative this indicated that the placebo had a positive effect
- placebo effects shown in conditions such as pain, nausea, asthma, and phobias
Authors' Conclusions
"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."
Important Notes
This Cochrane Review has a few strengths and weaknesses that contribute to the overall validity of the results. Firstly, the authors did a great job analyzing all relevant trials. However, because the authors did not have a focused clinical question and decided to include trials for ALL clinical conditions, it contributed to significant heterogeneity between studies which may alter the results. It would be interesting to see more comprehensive reviews based on disease state to try and decrease the variation between trials.
Therefore, more trials are needed to determine the clinical usefulness of placebos in practice. The referencing information for this study, as well as a few other interesting trials are listed in the additional resources page for further information.
This Cochrane Review has a few strengths and weaknesses that contribute to the overall validity of the results. Firstly, the authors did a great job analyzing all relevant trials. However, because the authors did not have a focused clinical question and decided to include trials for ALL clinical conditions, it contributed to significant heterogeneity between studies which may alter the results. It would be interesting to see more comprehensive reviews based on disease state to try and decrease the variation between trials.
Therefore, more trials are needed to determine the clinical usefulness of placebos in practice. The referencing information for this study, as well as a few other interesting trials are listed in the additional resources page for further information.
References:
1. Hrobjartsson A, Gotzsche PC. Placebo interventions for all clinical conditions. Cochrane Database Syst Rev. 2010;(1):CD003974
Images courtesy of:
http://www.tbase.com/corporate/large-format-printing
http://www.policyfromscience.com/blog/
1. Hrobjartsson A, Gotzsche PC. Placebo interventions for all clinical conditions. Cochrane Database Syst Rev. 2010;(1):CD003974
Images courtesy of:
http://www.tbase.com/corporate/large-format-printing
http://www.policyfromscience.com/blog/