Abdallah, Mohamed

Abstract Background: Placebo response is crucial in interpreting treatment efficacy in ulcerative colitis (UC) trials. While it has been broadly studied, it remains underexplored in trials involving the growing number of biologics and small molecules for ulcerative colitis. Methods: We systematically searched PubMed, Embase, Scopus, Web of Science, and Cochrane CENTRAL from inception to November 13, 2024. Eligible studies were induction-phase RCTs, including adult patients with moderate-to-severe UC who received a biologic and a small-molecule against a placebo. Primary outcomes were pooled clinical and endoscopic response and remission rates. Safety outcomes included adverse events (AEs), serious adverse events (SAEs), and withdrawal rates. Random-effect models were used for meta-analysis. Meta-regression identified predictors of placebo outcomes. Results: 26 induction RCTs with 3,937 placebo-treated patients were included. IL inhibitor trials had the highest placebo clinical response (36%) and endoscopic remission (21%), while JAK inhibitors had the lowest (21% and 2%). Overall placebo rates were 34% for clinical response, 8% for clinical remission, 19% for endoscopic response, and 11% for endoscopic remission. Adverse events occurred in 54%, SAEs in 8%, and withdrawals in 18%. Younger age and longer follow-up were linked to higher placebo responses; recent trials showed reduced endoscopic effects. Conclusion: These findings highlight the need to account for placebo variability in trial design and interpretation, particularly as biologic and small-molecule therapies continue to expand in UC treatment.