Lilly starts the COMMIT trials pairing tirzepatide with a biologic in inflammatory bowel disease

Eli Lilly has started two phase 3b trials, known as COMMIT, that give tirzepatide at the same time as mirikizumab, an interleukin-23 (IL-23) inhibitor used for inflammatory bowel disease, in adults who have both active IBD and obesity or overweight ^[1][2]. The trials are registered on ClinicalTrials.gov as NCT06937086 in ulcerative colitis and NCT06937099 in Crohn's disease ^[1][2].

Tirzepatide is the molecule sold as Mounjaro for type 2 diabetes and Zepbound for obesity. Mirikizumab is a biologic antibody that blocks IL-23, an immune signal involved in gut inflammation. The COMMIT program is unusual because it does not test the two drugs against each other. It tests whether adding a weight-loss medicine to a biologic changes how well the biologic controls bowel disease.

What the two trials are measuring

COMMIT-UC plans to enroll about 350 adults with moderately to severely active ulcerative colitis and obesity or overweight ^[1]. Its primary endpoint at week 52 is a composite: clinical remission of colitis plus at least a 10 percent reduction in body weight ^[1]. A participant has to hit both targets to count as a responder, which is a higher bar than either goal alone.

COMMIT-CD plans to enroll about 290 adults with moderately to severely active Crohn's disease and obesity or overweight ^[2]. It uses a similar composite but adds endoscopic remission, meaning healing visible when a doctor looks inside the intestine with a scope, on top of clinical remission and the weight target ^[2].

Primary completion, the point when the main outcome data are collected, is listed as April 2028 for one trial and May 2028 for the other ^[1][2].

The stated reason for combining the drugs is that obesity has been linked to worse response to biologic therapy in IBD ^[1][2]. Researchers have several theories for why that might happen, including differences in how drugs are distributed in the body and higher background inflammation from fat tissue, but the COMMIT trials are designed to test the practical question directly: if you treat the obesity too, does the gut disease respond better?

Several details are not spelled out in the registry entries available here, including the exact tirzepatide doses and titration schedule, the comparator arms, the number of study sites, and whether participants must have failed prior therapies. Those specifics are not yet known from these sources.

Why it matters for patients

Many people with ulcerative colitis or Crohn's disease also carry excess weight, and they have generally been treated for the two problems separately, often by different specialists. These trials are among the first large, randomized tests of running both treatments at once on purpose, rather than treating obesity as a side issue.

If the combination works, it could support a treatment approach in which a gastroenterologist considers weight as part of the IBD plan. If it does not, that would also be useful information, because it would suggest that weight loss alone does not unlock better biologic response.

Safety will be watched closely. GLP-1 based drugs like tirzepatide commonly cause nausea, vomiting, diarrhea and constipation, symptoms that can overlap with or be confused for an IBD flare. How that plays out in people whose bowels are already inflamed is a real question these trials should help answer, though safety findings are not available yet.

It is also worth being clear about what this is not. Tirzepatide is not approved for inflammatory bowel disease, and these are investigational studies. Nothing in the trial design changes current labeling or prescribing for either drug.

What happens next

Enrollment is the first milestone. Because both trials require a full year of treatment per participant, the timeline is long: primary completion is set for April 2028 in one study and May 2028 in the other ^[1][2]. Topline results would typically follow some months after that, with peer-reviewed publication later still. Interim safety monitoring happens throughout, but interim efficacy data are not expected to be made public.

People interested in participating can find eligibility criteria and site contacts on the ClinicalTrials.gov records for NCT06937086 and NCT06937099 ^[1][2].