Faecal microbiota transplantation (FMT) produces only transient improvement in IBS symptoms and the effects are no better than placebo at three months, a randomised controlled trial has shown.

When delivered by colonoscopy, a single treatment of FMT produced a significant improvement in IBS symptoms compared to baseline levels but the Finnish study involving 49 patients with IBS failed to reach its primary endpoint compared to a placebo treatment.

Using the ‘ambitious’ target of a 50 point reduction in IBS-SSS total scores, the study investigators found that this was achieved by half (11 out of 23) the patients in the FMT group at 12 weeks, and by a similar proportion (11 out of 26 patients) in the placebo group, with no significant difference between the groups.

The mean of IBS‐SSS total score was reduced significantly by 62 points in the FMT treatment group from the baseline value of 270 points down to 189 points at 12 weeks.

But there was no difference in IBS scores from baseline when followed up for a year, or for IBS scores with placebo at any time point up to 52 weeks.

The researchers noted that patients in the FMT treatment group showed a sustained change in microbiome profile over one year, which more closely resembled that of the FMT donor. Patients in the treatment group also showed significant reduction in stool water content compared to placebo.

Intriguingly, depression scores decreased in patients who had a reduction in IBS symptoms after FMT, but not in placebo‐treated patients who experienced a reduction in IBS symptoms.

The researchers said there had been five previous trials of FMT in IBS, which had provided conflicting results. They said it was notable that FMT given by colonoscopy generally produced improvements in IBS symptoms whereas FMT by capsule did not despite both producing favourable changes in the microbiota.

Accumulating evidence showed that FMT was effective as a treatment for recurrent C. difficile infection, but the results in IBS were inconsistent despite successful  long term engraftment of the transplanted microbiota.

“In the future, it may be possible to characterise the microbiota of a patient to choose the most suitable treatment strategy and to identify those subgroups of patients who would be more likely to benefit from microbiota enriching therapies,” they suggested.

“Nonetheless, since we did not detect a significant long‐term benefit of FMT over placebo in these patients, we conclude that a single FMT infusion via colonoscopy cannot be recommended as a treatment for IBS in clinical practice.”

The findings are published in Alimentary Pharmacology and Therapeutics.