Fecal Transplant Therapy Cuts Autism Symptoms 45% Two Years Out, Heads to Phase 3

Arizona State University researchers tracking children who received Microbiota Transplant Therapy (MTT) found benefits not only persisted but deepened over time. Initial 2017 and 2019 work showed 18 autistic children gained measurable improvements in behavior, communication, and GI symptoms after a bowel cleanse followed by seven to eight weeks of daily fecal microbiota transfers. At the two-year follow-up, professional evaluators measured a 45% drop in autism symptoms versus baseline, up from 24% at eight weeks. The share of participants rated as ‘severe’ fell from 83% to 17%, while 44% scored below the threshold for mild ASD entirely.

The working hypothesis ties the gut-brain axis to symptom severity: autistic children in the study had markedly lower microbial diversity than neurotypical peers, and 30-50% of people with autism experience chronic GI problems that appear to correlate with worse behavioral symptoms. Lead researcher Rosa Krajmalnik-Brown’s group has since patented a specific bacterial formulation, spun out Gut-Brain Axis Therapeutics, and completed a Phase 2 placebo-controlled trial in adults showing statistically significant improvements in GI symptoms, receptive language, and overall symptom averages versus placebo.

The team is now fundraising for Phase 3 trials required for FDA approval. The article is a 2025 update on a 2019 piece, and notable mainly because long-term durability and a successful Phase 2 readout are unusual for microbiome interventions, most of which have struggled to replicate early-stage results at scale.