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The following is a summary of “Placebo analgesia in physical and psychological interventions: Systematic review and meta-analysis of three-armed trials,” published in the November 2023 issue of Pain by Hohenschurz-Schmidt et al.
Uncertainties surrounding the magnitude of placebo effects in physical and psychological interventions hinder the interpretation of efficacy trials and treatment understanding.
Researchers conducted a retrospective study to compare pain outcomes in “sham” and non-exposure arms, quantifying the placebo effect of physical and psychological interventions.
They conducted RCTs involving treatment, ‘sham’ control interventions, and non-exposure groups, enrolling adults experiencing any pain. A pre-registered protocol existed (PROSPERO: CRD42023413324), and 12 databases from 2008 to July 2023 were searched. A descriptive analysis of trial methods and blinding, along with the assessment of the risk of bias, was carried out. Meta-analysis of pain measures at short-, medium-, and long-term utilized random-effects models of standardized mean differences (SMD). The studies were subgrouped based on the type of control intervention.
The results revealed the inclusion of seventeen Randomized Controlled Trials (RCTs). The short-term placebo effect averaged a small magnitude (0.21 Standardized Mean Difference [SMD], 95% CI 0.1–0.33, p = 0.0002, 1,440 participants). There was no observed heterogeneity (Tau2 = 0.1, I2 = 11%, P= 0.3), preventing the execution of meta-regression analyses for effect modifiers. Nevertheless, sub-group analyses indicated more significant placebo effects in manual control interventions compared to disabled devices and miscellaneous control interventions. In total, placebo analgesia contributed to 39% of the short-term effectiveness of treatments. No placebo effects were identified in the medium-term (7 RCTs, 381 participants) or long-term follow-up (3 RCTs, 173 participants).
They concluded that placebo analgesia has mechanisms and methodological implications, but its clinical value might be limited.
Source: onlinelibrary.wiley.com/doi/10.1002/ejp.2205
