Objective. Fibromyalgia (FM) is a nociplastic pain condition characterised by widespread pain, fatigue, cognitive dysfunction and multisystem involvement. Increasing evidence implicates the microbiota-gut-brain axis (MGBA) as a potential contributor to its complex pathophysiology. This scoping review maps contemporary evidence (2020–2026) on MGBA alterations in FM across microbial, metabolic, neuroimmune and translational dimensions. Methods. This review was conducted following the Arksey and O'Malley framework, as refined by Levac et al. and the Joanna Briggs Institute, and reported in accordance with PRISMA-ScR guidelines. A systematic search of PubMed/MEDLINE, EMBASE, Web of Science and Scopus identified studies published between January 2020 and March 2026. Eligible studies included primary clinical, translational and preclinical investigations evaluating microbiota composition, microbial metabolites, intestinal permeability, neuroimmune signalling, or microbiome-targeted interventions in FM. Narrative and systematic reviews were used only to contextualise findings and were not counted among the included studies. Results. Of 1,365 records identified, 39 studies were included in the final synthesis. Across studies, findings were heterogeneous but most frequently described alterations in gut microbiota composition, including reduced diversity and depletion of butyrate-producing taxa such as Faecalibacterium prausnitzii, along with shifts in Bifidobacterium and Prevotella. Key metabolic perturbations encompassed reduced short-chain fatty acid production and dysregulated tryptophan metabolism. Increased intestinal permeability and activation of neuroimmune pathways were additionally documented. Microbiota profiles were associated with clinically relevant outcomes including pain intensity, fatigue, and cognitive dysfunction. Interventional evidence remains limited but suggests emerging therapeutic potential. Conclusion. The MGBA represents a biologically plausible and integrative framework for FM, linking peripheral and central mechanisms. Current evidence remains heterogeneous and largely associative. Future research should prioritise longitudinal, mechanistically driven studies to advance microbiome-informed diagnostic and therapeutic strategies. © Copyright CLINICAL AND EXPERIMENTAL RHEUMATOLOGY 2026.
