This paper is a systematic review — meaning the authors gathered and analysed all the available human studies on one question — published in npj Parkinson's Disease in May 2026. The question: can faecal microbiota transplantation (FMT) help people with Parkinson's? FMT means taking stool from a carefully screened healthy donor, processing it, and delivering it into a patient's gut (by colonoscopy, enema, or capsule). The idea is that Parkinson's patients have an altered gut microbiome (the trillions of bacteria living in the intestine), and that correcting it might ease symptoms. The reviewers pooled 11 studies — five randomised controlled trials (RCTs, the gold standard), three observational cohort studies, one case series, and two single case reports — covering 236 people in total.
Here is what they found. Safety looked acceptable: the most common side effects were mild, short-lived gut complaints (bloating, diarrhoea, nausea). No alarming serious adverse events stood out. Constipation improved consistently across studies — a meaningful win, since it is one of the most troublesome non-motor symptoms in Parkinson's. Motor and other non-motor outcomes were mixed: one RCT showed motor benefit at 8–12 weeks, another only after a year, and others found no meaningful change. Crucially, most improvements in the RCTs hovered around or just barely exceeded the minimal clinically important difference (MCID) — the threshold at which a change is noticeable to a patient in daily life. Five studies also found shifts in which bacterial species were present after FMT, most notably an increase in bacteria from the Firmicutes group, though what that means for Parkinson's remains unclear.
For someone living with Parkinson's, the honest message is this: FMT is not ready to be prescribed for Parkinson's. The evidence base is small and inconsistent, and the procedures vary so much across studies (different donors, different delivery methods, different preparation) that results cannot easily be compared. The consistent improvement in constipation is real and worth discussing with a gastroenterologist. The motor signals are intriguing but fragile. What is needed now — and what the authors call for explicitly — are larger, well-designed RCTs with standardised protocols. That work is underway (see the related trials linked on the journal page), so a clearer answer may come within the next few years.