A Comprehensive Scientometric Analysis of Placebo and Nocebo Effects in Pain Research: From Placebo Mechanisms to Clinical Trials.

Placebo and nocebo phenomena are central in neuroscience, psychology, and clinical research, yet comprehensive bibliometric analyses remain limited. This study mapped placebo and nocebo research in pain, distinguishing mechanistic studies from randomised controlled trials (RCTs), using data from the Web of Science Core Collection up to March 2025, which yielded 1246 mechanistic studies and 35,134 RCTs. Analyses performed with the Bibliometrix R package included descriptive statistics, co-citation and keyword co-occurrence networks, and local citations to assess internal impact. Mechanistic studies grew 3.97% annually, focusing on expectation, conditioning, and pain modulation, with key contributions from Benedetti, Colloca, and Wager, concentrated in the USA, Germany, Italy, and the UK. RCTs grew 3.52% per year, emphasising systematic reviews and methodological standards (Jadad scale, PRISMA), led by Moore and Manchikanti, with the USA, China, and the UK dominating output. Co-citation analyses identified mechanistic clusters around opioidergic and dopaminergic pathways and prefrontal-cingulate circuits, and RCT clusters emphasising methodological rigour and pain outcomes. Keyword analyses highlighted pain, analgesia, and expectation as central themes, with emerging trends reflecting evolving clinical applications and innovative trial designs. This scientometric mapping underscores the dual role of placebo as a neurobiological phenomenon and methodological cornerstone, offering a comprehensive overview of the evolution, structure, and thematic organisation of placebo and nocebo research in pain.