ABSTRACT: BACKGROUND:The majority of patients with ulcerative colitis have mildly to moderately active disease. To inform the management of patients with left-sided or extensive mildly to moderately active ulcerative colitis, we assessed the comparative efficacy and tolerability of different therapies. METHODS:In this systematic review and network meta-analysis, we searched Epub, MEDLINE In-Process & Other Non-Indexed Citations, MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Scopus, and Web of Science from inception to Dec 14, 2015, and updated on MEDLINE on March 1, 2018, for randomised controlled trials in adults (age ?17 years) with left-sided or extensive mild to moderate ulcerative colitis. Studies were included if patients were treated with oral sulfasalazine, diazo-bonded 5-aminosalicylates (5-ASAs), mesalazine (low dose <2 g/day, standard dose 2-3 g/day, or high dose >3 g/day), controlled ileal-release budesonide, or budesonide multimatrix, alone or in combination with rectal 5-ASA therapy, and were compared with each other or placebo for induction or maintenance of clinical remission. The minimum duration of therapy was 4 weeks for trials of induction and 24 weeks for trials of maintenance therapy. We did pairwise and random-effects network meta-analysis using a frequentist approach, and calculated odds ratios (ORs) and 95% CIs; agents were ranked using surface under the cumulative ranking (SUCRA) probabilities. We used Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria to appraise quality of evidence. We examined heterogeneity with the I2 statistic. FINDINGS:Our search identified 1316 unique studies, from which 75 randomised trials with 12?215 patients were eligible for analysis. Based on 48 induction randomised trials (8020 participants) that met inclusion criteria, combined oral and rectal 5-ASAs (SUCRA 0·99) and high-dose mesalazine (>3 g/day; SUCRA 0·82) were ranked highest for induction of remission. Both interventions were superior to standard-dose mesalazine (2-3 g/day; failure to induce remission with combined oral and rectal 5-ASAs OR 0·41, 95% CI 0·22-0·77; high-dose mesalazine 0·78, 0·66-0·93) with moderate confidence in estimates. On the basis of 28 randomised trials (4218 participants) that met inclusion criteria, all interventions were superior to placebo for maintenance of remission; however, neither combined oral and rectal 5-ASAs nor high-dose mesalazine were superior to standard-dose mesalazine. INTERPRETATION:In patients with mildly to moderately active left-sided or extensive ulcerative colitis, combined oral and topical mesalazine therapy and high-dose mesalazine are superior to standard-dose mesalazine for induction of remission, but not maintenance of remission. Standard-dose mesalazine might be preferred for maintenance in most patients. FUNDING:None.