Gut bacteria transplant may ease constipation in Parkinson’s

Fecal microbiota transplantation (FMT), a technique for replacing gut bacteria, may help with gastrointestinal symptoms of Parkinson’s disease, particularly constipation, according to a review study.

While the technique was found to be generally safe and beneficial for gastrointestinal symptoms in Parkinson’s disease, “at this stage, there is no convincing evidence that FMT produces a clinically relevant motor or non-motor symptomatic improvement on a group basis, at least in the short to medium term,” the researchers wrote.

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June 9, 2026 News by Andrea Lobo

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Evidence on FMT remains limited

The researchers noted that available studies about FMT in Parkinson’s use a variety of different techniques, and many have methodological limitations. Future high-quality research could help clarify the potential benefits of FMT in this context.

The study, “Safety and efficacy of faecal microbiota transplantation in Parkinson’s disease,” was published in npj Parkinson’s Disease.

Parkinson’s is a neurological condition that leads to a variety of motor and nonmotor symptoms. Constipation and other gastrointestinal problems are among the possible nonmotor signs of the condition.

Parkinson’s and the digestive tract have a complex relationship. Not only can Parkinson’s cause gastrointestinal symptoms, but the bacteria and other microorganisms living in the intestines, collectively known as the gut microbiota, may influence certain disease processes. For example, the review noted that animal studies suggest that gut microbiota from people with Parkinson’s may promote inflammation and nerve degeneration.

These connections have led scientists to wonder whether altering the gut microbiota could be used as a treatment strategy for Parkinson’s. One way to do this is with FMT, which the researchers described as “an ultimate treatment for replacing the host microbiota with that of a healthy donor.”

There are several methods for performing FMT. Typically, they involve first collecting gut bacteria from donors’ stool. Patients receive the transplant as a capsule, an enema (a liquid placed into the rectum), or a procedure delivering the sample directly to the digestive system.

The team aimed to comprehensively examine existing research about FMT in Parkinson’s, which remains limited. “This review examines the current evidence on FMT in [Parkinson’s disease] concerning safety, efficacy, and microbiome changes, and analyses the data in the perspective of recommendations for future studies in this field,” they wrote.

Constipation improved in most studies

They found 11 published studies on this topic. Across studies, the FMT protocols, including donor selection and delivery method, differed considerably. Different studies also used different sets of metrics for quantifying symptoms. Despite this variability, the team examined commonalities and differences in the reported results.

“The most consistent reported benefit was improvement of gastrointestinal functions, as determined both by subjective and objective measures,” the researchers wrote. Nine studies reported constipation improvements after FMT.

Another common finding was that the transplant procedures were generally safe and well tolerated. No serious treatment-related safety concerns arose in the studies.

Beyond this, results were less consistent. Several uncontrolled studies, including case reports, reported improvements in non-gastrointestinal Parkinson’s symptoms after FMT. These benefits in motor and nonmotor symptoms were “rarely observed” in trials with control groups.

Two studies reported a certain degree of improvement in motor function after treatment, but the timelines were inconsistent. One found significant differences from the control group at eight and 12 weeks after treatment. The other found significant differences only at 12 months.

Differing donor strategies and transplant delivery techniques could have affected these results. Given the limited number of studies and methodological variability, the researchers couldn’t assess these potential effects in detail. Based on overall trends, however, they suggested that fresh or frozen FMT suspensions — liquid mixtures used for the transplant — may be preferable for future studies, while capsule- or enema-based approaches showed less consistent effects.

Placebo effect may complicate findings

Another factor that may have affected results was the placebo effect. “Interestingly, the placebo groups in [controlled studies] often displayed significant improvements,” the team noted. This means that even if the FMT groups also improved, those gains could not be clearly attributed to FMT itself.

The researchers suggested that as experiments into FMT for Parkinson’s disease continue, trials should focus on implementing appropriate controls and standardizing efficacy metrics. Longer-term follow-up could also help strengthen results.

Given that Parkinson’s is a chronic and progressive disease, “a single FMT … might not be sufficient to provoke a durable and significant response,” the team wrote. Future studies could test repeated FMTs over a longer period to see whether this approach leads to more durable effects.