Prospective, double-blind, randomized, placebo-controlled studies are considered to provide the highest quality of interventional evidence. This meta-analysis summarizes the frequencies of adverse events according to the Medical Dictionary for Regulatory Activities (MedDRA) in the placebo arms of 101 such studies in rheumatoid arthritis, including a total of 17,150 patients in the placebo arms and 37,819 patients in the verum arms. Placebo-treated patients reported more than one adverse event in a median of 55.0%, 65.5%, and 72.5% (compared to 72.3% in the verum arms), and a serious adverse event in 2.5%, 5.8%, and 8.6% (compared to 5.9% in the verum arms), with stable doses of corticosteroids, conventional synthetic disease-modifying antirheumatic drugs (DMARDs), and biological DMARDs as background therapies, respectively. Odds ratios were comparable between placebo and verum arms for nausea (1.00 with 95% confidence interval (CI) 0.86-1.17), for hepatobiliary disorders (1.08 with CI 0.85-1.36), for abnormal hepatic functions (1.09 with CI 0.83-1.44), and general disorders and administration site conditions (1.39 with CI 0.95-2.03). A publication bias has to be assumed for nausea (p = 0.018; Egger's test), diarrhoea (p = 0.022), and serious infections and infestations (p = 0.009). In conclusion, patients should be aware that "adverse events" may occur even with placebo medication, independent from an additional verum medication added to the background therapy. Further studies are warranted to respect and overcome the psychological and other issues related to these placebo-related "adverse events".
Keywords: adverse effects; complementary medicine; musculoskeletal diseases; nocebo effect; placebo-controlled trial; rheumatology; shared decision-making.