In the recent decade, ulcerative colitis (UC) as a chronic inflammatory bowel disease has a growing incidence and prevalence in the world. Probiotics might be a promising approach to improve ulcerative colitis by favorably modifying the gut microbiota.

A double-blind, randomized, placebo-controlled, parallel-group clinical trial was conducted on sixty patients with mild/moderate ulcerative colitis. Participants were administered either placebo (n = 30) or a multi-strain probiotic (n= 30) for 16 weeks. Clinical disease status, via Lichtiger and Mayo questionnaires, was assessed at baseline and after 8 and 16 weeks of intervention. Also, fecal calprotectin was measured before and after the study period. Within and between groups, comparisons were made using per-protocol (PP) and intention-to-treat (ITT) approaches, and a P-value≤0.05 was considered a statistically significant level.

Of the sixty patients who agreed to participate in the study, 18 dropped out during the study due to low compliance and gastrointestinal complications. The two groups were comparable in baseline variables (P>0.05). During the study, the within and between groups’ differences of calprotectin and Mayo scores were not statistically significant. Although the mean score of Lichtiger was significantly decreased in the probiotic group during the study period (P = 0.001), no statistically differences compared with placebo group were seen.

Our study elucidated that probiotic supplementation does not significantly improve UC patients, which may be due to the strain and dose administered. Future research should focus on the best effective strains and doses for ulcerative colitis.