A two-year clinical study led by Arizona State University has found that fecal microbiota transplants (FMT) can reduce autism spectrum disorder (ASD) symptoms by as much as 45%. The research, published on April 21, 2025, marks a significant advancement in exploring the gut-brain connection and its potential to treat neurodevelopmental conditions. The study is now progressing to Phase 3 human trials. 1
The study, conducted by researchers Rich Haridy and Nick Lavars, involved a cohort of participants diagnosed with autism. Over the two-year period, the team observed a 45% reduction in core autism symptoms, including improvements in social communication and repetitive behaviors. The findings build on earlier research suggesting a link between gut microbiome diversity and neurodevelopmental disorders. The therapy involves transplanting fecal matter from healthy donors to recipients to restore microbial balance. 1
Arizona State University’s research team highlighted the long-term benefits of the treatment, noting sustained improvements in participants even after the intervention concluded. The study’s results align with growing evidence that the gut microbiome plays a critical role in brain function and behavior. While fecal transplants are already approved for treating recurrent Clostridioides difficile infections, their application in autism remains experimental. The Phase 3 trials will aim to validate these findings in a larger population. 1
The connection between gut health and autism has been a subject of scientific inquiry for years. Previous studies have documented differences in the gut microbiomes of individuals with autism compared to neurotypical individuals. This study’s success in reducing symptoms by nearly half underscores the potential of microbiome-based therapies. Researchers emphasized that while the results are promising, further investigation is needed to understand the mechanisms driving these changes. 1
Fecal microbiota transplants work by introducing a diverse range of beneficial bacteria into the recipient’s gut. The procedure typically involves processing donor stool into a liquid or capsule form, which is then administered to the patient. In this study, participants underwent a multi-week regimen of transplants, followed by a two-year observation period. The 45% reduction in symptoms was measured using standardized autism diagnostic tools, including the Childhood Autism Rating Scale (CARS). 1
The study’s authors, Rich Haridy and Nick Lavars, noted that the improvements were not limited to behavioral symptoms. Participants also reported enhancements in gastrointestinal (GI) issues, which are commonly associated with autism. Up to 50% of individuals with autism experience chronic GI problems, and the study suggests that addressing gut health may alleviate both physical and neurological symptoms. The Phase 3 trials will further explore this dual benefit. 1
While the study’s results are groundbreaking, researchers caution that fecal transplants are not yet a standard treatment for autism. The therapy is still considered experimental for neurodevelopmental conditions, and its long-term safety and efficacy require validation through larger clinical trials. The U.S. Food and Drug Administration (FDA) has not approved FMT for autism, though it is closely monitoring developments in the field. 1
The study’s progression to Phase 3 trials signals growing confidence in microbiome-based therapies for autism. If successful, the treatment could offer a non-invasive alternative to existing interventions, which often focus on behavioral therapies and medications. The research team at Arizona State University is collaborating with other institutions to expand the trial’s scope and ensure diverse participant representation. 1