Background Beneficial effects from placebo have been documented in many diseases, such as osteoarthritis and Parkinson's disease (1), but how effective placebo is in the treatment of fibromyalgia (FM) is unknown. Many published randomised controlled trials (RCTs) have compared a variety of treatments to placebo in participants with FM. It is feasible to study the magnitude of the placebo effect observed within these trials.
Objectives  to determine whether placebo is effective for FM;  to identify the possible determinants of the magnitude of the placebo effect
Methods We searched Medline, PubMed, Web of Science, EMBASE, and CINAHL for RCTS in FM that included either a placebo group or a no treatment (observation only) group. The placebo effect was measured as a standard mean change, or effect size (ES) of pain and other outcomes from baseline (ie, mean change from baseline divided by the standard division of the change) and compared to change in these outcomes in no treatment control groups. Meta-analysis was undertaken to combine data from different studies. Subgroup analysis was conducted to identify possible determinants of the magnitude of the placebo effect.
Results 3375 studies were found from the literature search. After scrutiny, 204 trials met the inclusion criteria. In total 13,968 participants were included from all trials, (mean age 49.2 years; 95.4% women). Participants who took placebo in the trials had significant improvements in pain, fatigue, sleep quality, physical function, and other main outcomes, while participants in the no treatment controlled group remained unchanged. The overall ES of placebo for pain is clinically moderate (ES=0.47, 95%CI 0.37 to 0.56). The ES increased with increasing strength of the active treatment, older age and higher baseline pain severity, but was lower in women than men and lower in RCTs with longer treatment periods.
Conclusions Although considered a hard-to-treat condition, people with FM treated with placebo can show significant improvement in pain and other outcomes. Several variables influence the magnitude of this effect. Optimisation of such contextual response could have relevance to clinical care.
Zhang W, Robertson J, Jones AC, Dieppe PA, Doherty M. The placebo effect and its determinants in osteoarthritis: meta-analysis of randomised controlled trials. Annals of the Rheumatic Diseases 2008;67(12):1716-23.
Acknowledgements I'd like to thank Dr. Weiya Zhang and Prof. Michael Doherty for their supervision and Arthritis Research UK for sponsoring this research.
Disclosure of Interest : None declared