CHICAGO — Fecal microbiota transplantation (FMT) was associated with short-term improvements in both motor and non-motor symptoms in patients with Parkinson’s disease (PD).

Results of a systematic review and meta-analysis of eight studies, which included more than 200 participants, showed that patients with PD who underwent FMT had significant improvements in motor function, quality of life, and constipation. However, these benefits began to diminish 12-24 weeks later.

Still, “it was amazing to find a difference in motor outcomes in Parkinson’s,” study co-investigator Rebeca Silva, a medical student at the Federal University of Paraíba in João Pessoa, Brazil, told Medscape Medical News.

She added that because constipation is an early symptom of PD, FMT may be most effective in patients with early-stage disease. However, larger trials are needed to confirm these findings, she added.

The study was presented on April 21 at the American Academy of Neurology (AAN) 2026 Annual Meeting.

The Gut-Brain Axis and PD Link

“Altered gut microbiota composition has been implicated in PD pathogenesis via the gut-brain axis,” the investigators noted.

FMT involves transferring screened donor gut bacteria into a recipient’s gastrointestinal tract. As such, restoring microbial balance through FMT has been explored as a potential way to alleviate motor dysfunction and other symptoms.

However, findings to date have been mixed, and “the magnitude and durability of the clinical effects remain uncertain,” the researchers noted.

As previously reported by Medscape Medical News, a small randomized controlled study published in 2024 in JAMA Neurology showed that while the procedure was safe, it was not linked to a clinically meaningful improvement in symptoms compared with placebo.

To evaluate the efficacy and safety of FMT in PD, the investigators conducted a systematic review and meta-analysis of studies through September 2025, including five randomized controlled trials and three observational studies (n = 220).

Outcome measures included motor function on the Unified Parkinson’s Disease Rating Scale Part III (UPDRS III), activities of daily living on UPDRS II, quality of life on the Parkinson’s Disease Questionnaire-39, Wexner constipation scores, and gastrointestinal adverse events.

Pooled analysis showed that FMT was associated with significant improvements in motor function (mean difference [MD], -9.7; 95% CI, -16.8 to -2.5), quality of life (MD, -13.95), and constipation (MD, -3.9) compared with placebo, but benefits peaked at 4 weeks and then decreased at 12-24 weeks. Improvements in activities of daily living were not significant.

Additional analyses showed that studies with larger sample sizes were associated with greater improvements in constipation, while longer follow-up was linked to greater improvements in UPDRS II scores.

FMT was associated with a higher overall rate of gastrointestinal adverse events than placebo (risk ratio, 3.1), although these events were generally mild, the investigators reported.

Overall, the findings suggest that targeting the gut microbiome may offer a viable therapeutic approach, but the short-lived nature of the benefits could limit its clinical utility, they noted.

Larger, well-designed trials are needed to better define optimal treatment protocols and assess long-term efficacy, the investigators added.

‘Hard to Digest’

As interest in the gut microbiome has grown, so has attention to FMT as a potential therapy for PD, said Abhimanyu Mahajan, MD, associate professor of neurology and rehabilitation medicine at UC Health in Cincinnati.

Mahajan, who is also chair of the AAN Movement Disorders Section and was not involved in the study, pointed out that while the JAMA Neurology study showed safety but no improvement in PD symptoms, another study reported mild motor benefit in individuals with early-stage PD. Also, a study published in February reported some benefit in non-motor features, but no motor benefit.

“While we await the full manuscript, results from [the current] abstract report heterogeneous and transient benefit. I agree with the researchers on the need for larger, well-controlled trials for determination of therapeutic benefit,” he told Medscape Medical News.

“With the data available currently, a conclusive answer would be hard to digest,” Mahajan added.

The study was independently supported. Silva and Mahajan reported no relevant financial relationships.