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Differential effectiveness of placebo treatments: a systematic review of migraine prophylaxis. 

Meissner K, Fässler M, Rücker G, Kleijnen J, Hróbjartsson A, Schneider A, Antes G, Linde K.

DESCRIPTION:

In an advance for placebo research, a recent systemic meta-analysis has found differences in the nonspecific treatment effect of placebo control groups across treatment interventions in randomized controlled trials for migraine prophylaxis. This study shows that sham acupuncture and sham surgical intervention have a stronger placebo effect than oral pharmacological placebo. The authors “[focused] on a single condition with well-defined diagnostic criteria and outcome measures” in order to clearly confirm previous findings on the relative strength of acupuncture placebo treatments. They extend this finding further, since this study's “results suggest that the response to sham acupuncture and sham surgery can be as great as the mean response to active drugs.”

In this systemic meta-analysis, Meissner et. al. analyzed 79 randomized trials on migraine prophylaxis. The included trials compared an experimental intervention and a placebo control over a period of at least 8 weeks after randomization. The authors found that sham interventions involving a physical procedure (sham surgery and sham acupuncture) were the only significant predictors of response in placebo groups in multivariate analysis (P= .005 and P= .001, respectively). Network meta-analysis confirmed that more patients reported response in sham acupuncture groups than in oral pharmacological placebo groups (odds ratio, 1.88).

The study calculates pooled random-effects estimates according to the type of placebo for the proportions of treatment response, defining a treatment responder as someone who exhibits a reduction in migraine attack frequency by at least 50%. Meta-regression analyses identify sources of heterogeneity, and a network meta-analysis combines direct and indirect comparisons within and across trials, with further analyses for continuous outcomes. The study was funded by the German Ministry of Education and Research and spearheaded by Dr. Karin Meissner of the Institute of Medical Psychology at Ludwig-Maximilian-University in Munich, Germany.

This well-executed study helps clear up one aspect of the muddied waters of acupuncture efficacy studies. In what has been termed an “efficacy paradox,” although an intervention may have a higher level of clinical effectiveness compared to standard care, if the relative proportion of the placebo effect is stonger within the intervention, then the efficacy of that intervention can become statistically insignificant. Dr. Meissner wrote in an email to Reuters Health, “Even though acupuncture is associated with a smaller specific effect when compared to its placebo than are oral pharmacological drugs, the total improvement after sham surgery and sham acupuncture is as large as after active drugs...Since we know today that placebo effects are not imaginary, but real neurobiological phenomena, physicians should not be afraid to try to harness placebo effects and to communicate this benefit to their patients.(1)”

The authors conclude, “although our study cannot prove that this association is causal, the results support the notion that some placebo treatments can trigger clinically relevant responses.” This then encourages the further investigation of “treatment options whose contexts vary strongly...in placebo-controlled trials and head-to-head comparisons. Otherwise, treatments with small specific effects greater than those of their sham controls are withheld from patients even though they work better than standard treatment.”

This study prompts clinicians to compare placebo effect to treatment effect within a type of intervention, “such as surgery treatment with sham surgery treatment and pill with sham pill,” according to JAMA Internal Medicine editor Rita Redberg. Clinicians must look beyond the efficacy paradox when analyzing treatment options for a specific condition.

1. Brooks, Meghan. “Type of placebo matters in trials of migraine prophylaxis.” News Daily. Reuters, 16 Oct 2013. Web. 11 Dec 2013.

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