As new therapies for the treatment of Crohn's disease (CD) are approved, there is an increasing need for evidence that clarifies their positioning and sequencing.

Comparative effectiveness research (CER) aims to inform physicians' decisions when they choose which intervention (drug or treatment strategy) to administer to their patients. Pragmatic head-to-head trials represent the best tools for CER, but only a few have been published in the IBD field. Network meta-analyses can point toward the superiority of one drug over another, but they do not reflect everyday clinical practice. Finally, real-world evidence complements that coming from head-to-head trials and network meta-analyses, assessing the real-life effectiveness of therapeutic interventions.

There is insufficient evidence to create a definitive therapeutic algorithm for CD, but some general considerations can be made. Anti-TNF-α agents seemingly represent the most 'sustainable' first-line choice, considering benefit-harm ratio and costs; vedolizumab, ustekinumab, and risankizumab may be considered as first-line choice when safety issues become prominent. In the event of pharmacodynamic failure, out-of-class swap is to be preferred - possibly with anti-IL23p19 as the best option, with unclear data regarding upadacitinib positioning; a second anti-TNF-α could be considered, as a second choice, after pharmacokinetic failure.

As our comprehension of the pathogenic mechanisms of inflammatory bowel disease (IBD) increases, the therapeutic armamentarium for its treatment can expand, and novel target therapies join the treatment pipeline. Interleukin (IL)-12 and IL23 are two key cytokines responsible for promoting and perpetuating bowel inflammation in IBD. Ustekinumab is a monoclonal antibody directed against the shared p40 subunit of both cytokines, and it was recently approved for the treatment of ulcerative colitis (UC). In the pivotal phase III UNIFI trial, ustekinumab showed a superiority over placebo in both clinical and endoscopic outcomes; furthermore, it was characterized by a favorable safety profile, with a similar rate of adverse events as compared with placebo. Recent evidence from real-life experiences have started accumulating, generally confirming the effectiveness and safety figures emerged from the registration studies. However, most of these observational studies enrolled multirefractory patients; moreover, comparative data with other target therapies are lacking, leaving physicians without clear indications about the appropriate positioning of ustekinumab in the therapeutic pipeline for UC. This review examines the basis of targeting IL12-23 in UC therapy and summarizes the data from both clinical trials and real-life studies, to highlight the main evidence already available and the research gaps that need to be filled for the optimal usage of ustekinumab in UC.