Tirzepatide trial in type 1 diabetes adds 20-month arm and 465 adults
The companion study makes this the largest test of a dual GIP/GLP-1 agonist in type 1 diabetes, a group these drugs are not approved to treat; primary completion is listed for November 2026.
A second trial testing tirzepatide in adults with type 1 diabetes is underway, adding a longer treatment period to a research program that together is expected to enroll 1,370 people [1]. The new study, called SURPASS-T1D-2, is registered on ClinicalTrials.gov as NCT06962280 [1].
The trial is randomizing 465 adults who have type 1 diabetes and also have obesity or are overweight to either tirzepatide or a placebo [1]. Participants are to be treated for about 20 months [1]. The main measurement, or primary endpoint, is the change in HbA1c — a blood test that reflects average blood sugar over roughly the previous three months — at week 40 [1].
SURPASS-T1D-2 is the long-term companion to SURPASS-T1D-1 [1]. With the two studies combined, 1,370 people are to take part, which the listing describes as by far the largest test of a dual GIP/GLP-1 agonist in type 1 diabetes [1]. Tirzepatide is the molecule in Mounjaro, approved for type 2 diabetes, and Zepbound, approved for obesity. It is not approved for type 1 diabetes.
Type 1 diabetes is treated with insulin. The two SURPASS-T1D studies enroll only adults who have type 1 diabetes plus overweight or obesity, so any findings would describe that group rather than everyone with type 1 diabetes [1].
Why it matters for patients
Type 1 diabetes is a different disease from type 2, and the GLP-1 and dual GIP/GLP-1 drugs now widely used for type 2 diabetes and for weight loss have not been cleared for it. Whether tirzepatide lowers blood sugar, changes weight, or alters how much insulin someone needs in type 1 diabetes has not been reported [1]. No results from either trial have been posted [1].
That means people with type 1 diabetes who want to know if these drugs could help them are still waiting on evidence, and no safety information specific to type 1 diabetes has been disclosed [1]. Questions that often come up for patients — whether such a drug could reduce insulin doses, how it would interact with insulin, and what it would cost — are not addressed in the trial listing and have not been reported [1].
The size of the program is itself notable. Testing a drug in 1,370 people with type 1 diabetes is a larger effort than the earlier, smaller studies that have looked at GLP-1 drugs in this population, and the 20-month treatment period in SURPASS-T1D-2 is designed to show what happens over a longer stretch than a few months [1].
What happens next
The SURPASS-T1D-2 listing gives a primary completion date of November 2026 [1]. The week-40 primary endpoint is measured well before that date, but when any results will be released, and whether the trial sponsor will seek FDA approval for type 1 diabetes, has not been disclosed [1].
SURPASS-T1D-1, the companion study, has also been testing tirzepatide in adults with type 1 diabetes [1]. Its enrollment, its duration, and its own completion date are separate from the figures listed for SURPASS-T1D-2 [1]. Until results from either trial are posted, the effect of tirzepatide in type 1 diabetes remains unknown [1].
Sources
Semaglutides.org provides information only, not medical advice. Talk to a licensed provider about your own care before making changes. Some telehealth links are affiliate links and are labeled where they appear.