Efficacy of gut microbiota-based therapy for autism Spectrum Disorder and attention Deficit Hyperactivity Disorder: a systematic review and meta-analysis

The gut-brain axis is an emerging therapeutic target for neurodevelopmental conditions such as Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD). However, the overall efficacy of gut microbiome-based interventions remains unclear. This systematic review and meta-analysis, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines, aimed to synthesize the evidence on these interventions. Fifteen randomized controlled trials (RCTs) were identified from 1,080 records across PubMed, Embase, Web of Science, Cochrane, PsycInfo, MEDLINE, and ClinicalTrials.gov through August 2024. Interventions included probiotics, prebiotics, dietary changes, and fecal transplants. Using random-effects models, pooled analysis showed a small but significant overall benefit of gut microbiota-based interventions (Standardized Mean Difference, SMD = -0.12; 95% Confidence Interval, CI: −0.19 to −0.04), with low heterogeneity (I2 = 5.9%). Effects differed by disorder: ADHD demonstrated greater improvement (SMD = -0.24; 95% CI: −0.42 to −0.06; I2 = 50.4%) compared to ASD (SMD = -0.05; 95% CI: −0.15 to 0.04; I2 = 0%). Duration-specific effects emerged: 8-week interventions showed significant outcomes (SMD = -0.32; 95% CI: −0.58 to −0.06), while shorter or longer durations lacked significance. Acceptability analysis from eight studies revealed comparable dropout rates between intervention and control groups (ASD: Risk Ratio, RR = 1.002; ADHD: RR = 0.943), with no serious adverse events reported. Subgroup analyses identified participant age, diagnosis type, and geographic location as heterogeneity sources. Despite methodological limitations and small sample sizes, findings suggest gut microbiome modulation may offer a safe adjunctive therapy, particularly for ADHD, with optimal effects emerging at 8 weeks. The gut-brain axis appears promising for neurodevelopmental disorders, but current evidence remains preliminary. Future research should prioritize large-scale RCTs with standardized protocols, mechanistic investigations, and long-term follow-up to establish clinical guidelines and clarify biological pathways. Findings underscore the need to tailor interventions to specific disorders and optimize treatment duration.