Efficacy and safety of probiotic supplementation in PsA—a randomized controlled trial

Objectives: To evaluate the clinical efficacy and safety of a multispecies probiotic in patients with PsA in moderate disease activity. Methods: In this single-centre, randomized, double-blind, placebo-controlled trial (RCT), 66 PsA patients with moderate disease activity (Psoriatic Arthritis Disease Activity Score [PASDAS] > 3.2 to <5.4) on stable immunomodulatory therapy were randomized 1:1 to receive either a multispecies (Lactobacillus, Bifidobacterium) probiotic or placebo for 12 weeks. The primary outcome was treatment response at week 12, defined as achieving low disease activity or remission (PASDAS ≤3.2) without treatment change. Secondary outcomes included gut permeability markers, immune cell and microbiome composition. Analyses were conducted per a modified intention-to-treat (only complete cases for primary outcome), with sensitivity analyses using multiple imputation, per-protocol datasets and qPCR-based detection of the probiotic strains in stool (adherence). Results: Fifty-six participants were included in the main analysis. Thirteen (43%) participants in the probiotic group and 17 (65%) in the placebo group achieved the primary outcome (P = 0.167). The corresponding odds ratio was 0.4 (95% CI 0.13–1.18). Patient-reported pain and global assessment were the main PASDAS components improving over time, with no between-group differences. No differences were observed in secondary clinical outcomes, gut permeability markers (zonulin, calprotectin, alpha-1-antitrypsin), immune cell profiles or stool microbiome composition between the groups at week 12. No serious adverse events related to the study product were reported. Conclusion: In this first RCT investigating probiotic supplementation in PsA, probiotic treatment did not show superiority over placebo in achieving treatment response, or altering gut microbiome, or permeability. © The Author(s) 2026. Published by Oxford University Press on behalf of the British Society for Rheumatology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.