The Use of Probiotics for Pain Reduction in Patients With Fibromyalgia: A Systematic Review

Background: Probiotics represent a potential therapeutic option for patients with fibromyalgia. Emerging evidence suggests that the gut-brain axis can modulate neuronal-mediated pain symptoms. This systematic review evaluates the efficacy of probiotic supplementation for pain reduction in patients with fibromyalgia. Methods: Following the PRISMA 2020 guidelines, the databases search included MEDLINE (PubMed), Embase, Scopus, Web of Science, Cochrane CENTRAL, and ClinicalTrials.gov up to April 2025. Eligible studies included randomized controlled trials evaluating the use of probiotics for pain management in adults (age ≥18 years) with fibromyalgia. Interventions were multistrain probiotics for 8–12 weeks; outcomes included VAS pain, FIQ/FIQR, and SF-36. Studies involving pediatric populations, other chronic pain conditions, or lacking pain outcomes were excluded. Risk of bias was assessed using the Cochrane Risk-of-Bias 2 tool. (OSF Registries: https://doi.org/10.17605/OSF.IO/KHVR7) Results: Of 923 records, 3 double-blind, placebo-controlled RCTs (2018–2024; n=213; 198 women; ages ~46–55; Spain/Turkey) met eligibility criteria and were included. Pain was assessed as a primary and secondary outcome. One trial showed a greater VAS pain reduction with probiotics at 8 weeks (per-protocol; p=0.032; moderate effect), while the other two reported no between-group differences in pain; SF-36 improvements favoring probiotics/prebiotics appeared in one study only. Heterogeneity in strains, dosing, and outcome reporting precluded meta-analysis. Overall risk of bias assessment showed some concerns or high, driven mainly by selective reporting. Conclusions: Overall, partly due to the limited number of studies for this topic, the evidence for pain improvement using VAS, FIQ (FIQR), or SF-36 remains weak and inconclusive. Furthermore, the risk of bias assessment indicates the need for cautious interpretation of the current findings. It underscores the need for larger, high-quality randomized controlled trials to generate more reliable evidence regarding the efficacy of probiotics in managing pain among patients with fibromyalgia.