Design: Phase 3, randomised, double-blind, placebo-controlled trial
Population: 448 adults aged 18–65 with moderate-to-severe IBS
Primary outcome: ≥75-point fall in IBS-SSS at 90 days
Effect: 40% vs 38%; difference 1.9 points (95% CI −8.1 to 12.0)

REFIT2 was a phase 3 double-blind trial at five Norwegian hospitals. It enrolled 450 adults aged 18–65 with moderate-to-severe IBS by Rome IV criteria and randomised them 2:1 to a single rectal enema of donor stool or of their own stool as placebo.

At 90 days, 40% of the donor group and 38% of the placebo group had an improvement of at least 75 points on the IBS Severity Scoring System (difference 1.9 percentage points, 95% CI −8.1 to 12.0). Adverse events were similar.

Earlier smaller trials had been mixed. This one is large and well blinded, and it is negative. It suggests microbiota change alone is not enough to shift IBS symptoms, and it is a reason to steer patients away from unregulated FMT offered for IBS.

Do not recommend faecal microbiota transplantation for IBS outside a trial.
Tell patients that about four in ten improved with their own stool — placebo response in IBS is large.
Keep to established IBS care: diet (including low-FODMAP), gut-directed psychological therapy and symptom-targeted drugs.
Faecal transplantation remains indicated for recurrent Clostridioides difficile infection, which is a different question.

Why it matters

It closes off a treatment many IBS patients ask about, and highlights how much of IBS improvement is placebo response.

The statistics, in plain English

The difference of 1.9 percentage points has a confidence interval from −8.1 to 12.0, which crosses zero. The trial rules out a large benefit, though not a small one.