Comparative efficacy of gut microbiota-targeted therapies for motor and non-motor symptoms in Parkinson's disease: a systematic review and network meta-analysis

Abstract

Gut dysbiosis may contribute to Parkinson's disease (PD) through the microbiota-gut-brain axis. Probiotics, synbiotics, and fecal microbiota transplantation (FMT) have been studied as potential treatments, but their comparative effects remain uncertain. We searched trial registries and electronic databases from inception to April 1, 2026 for randomized controlled trials of gut microbiota-targeted therapies in PD. We performed a frequentist network meta-analysis. Risk of bias was assessed with Cochrane RoB 2, and confidence in the evidence was assessed with CINeMA. Treatment rankings were summarized using SUCRA values. Nineteen RCTs involving 1,156 participants and five treatment options (FMT, probiotics, synbiotics, routine care, and placebo) were included. Probiotics increased spontaneous bowel movement (SBM) frequency compared with placebo (MD = 1.93, 95% CI: 0.23 to 3.64; SUCRA = 88.3%). In the oral-administration subgroup, probiotics (MD = 2.01, 95% CI: 0.64 to 3.39) and synbiotics (MD = 1.23, 95% CI: 0.01 to 2.45) increased SBM frequency. No active treatment significantly improved MDS-UPDRS III scores compared with placebo, although synbiotics and FMT had higher SUCRA rankings. Evidence certainty was Moderate for oral probiotics on SBM frequency and Low to Very Low for motor function and quality of life. Oral probiotics improved SBM frequency in patients with PD. Evidence for motor function and quality of life was uncertain, and the higher rankings of FMT and synbiotics should be considered exploratory. Larger head-to-head randomized trials are needed. https://www.crd.york.ac.uk/PROSPERO/recorddashboard .