Tirzepatide and Type 1 Diabetes: What the Off Label Studies Show About Weight, Insulin Doses and Low Blood Sugar

Tirzepatide is not approved for type 1 diabetes, yet a growing number of adults with type 1 diabetes and obesity are prescribed it off label, and the early evidence on tirzepatide in type 1 diabetes shows meaningful weight loss alongside lower insulin needs. The first randomized trial, published in Diabetes Care in 2026, found 8.7 kg more weight loss than placebo after 12 weeks, together with a 35.1% relative drop in daily insulin. Because that trial enrolled only 24 people, most of the picture still comes from clinic data.

Is tirzepatide approved for type 1 diabetes?

Tirzepatide is not FDA approved for type 1 diabetes. The current Mounjaro label, revised in August 2026, indicates it "as an adjunct to diet and exercise to improve glycemic control" in people with type 2 diabetes from age 10. The Zepbound label covers long term weight reduction in adults with obesity, or overweight with a weight related condition, and obstructive sleep apnea.

Some clinicians prescribe tirzepatide to adults with type 1 diabetes who also meet the weight criteria, which means that dosing and monitoring rules for this group have not been set by large trials. Our guide to who qualifies for tirzepatide covers the populations the labels do include.

What did the first randomized trial of tirzepatide in type 1 diabetes find?

The first randomized trial found that tirzepatide clearly outperformed placebo for weight loss over 12 weeks in adults with type 1 diabetes and obesity. Snaith and colleagues in Sydney ran a double blind phase 2 trial in adults with a BMI over 30, giving tirzepatide 2.5 mg for 4 weeks and then 5.0 mg for 8 weeks, or placebo, alongside usual insulin. Of the 24 people enrolled, 22 completed the study.

People on tirzepatide lost a mean 10.3 kg versus 0.7 kg on placebo, a difference of 8.7 kg (8.8% weight loss), and 45% lost at least 10% of body weight versus 0% on placebo. HbA1c improved by 0.4% versus placebo, a borderline result, and total daily insulin fell by 24.2 units/day versus 0.3 units/day, with no significant adverse events in either group. Because the trial was short and small and used only the two lowest doses, it cannot show what happens over years or at higher doses.

What do real world studies show about weight loss?

Real world studies of adults with type 1 diabetes on tirzepatide report weight loss of roughly 10% to 18% at one year. All are retrospective studies from specialist clinics, so they describe selected patients rather than proving cause and effect.

• Barbara Davis Center, Colorado. Garg and colleagues followed 62 adults on tirzepatide for 1 year against 37 matched controls; the mean weekly dose rose from 5.6 mg to 9.7 mg, average weight loss was 18.5%, and HbA1c fell by 0.67%.
• Mayo Clinic. Rivera Gutierrez and colleagues reviewed 51 adults, whose weight loss reached 12.2% at 12 months among the 26 people with data at that point, while HbA1c fell by 0.9%.
• Dasman Diabetes Institute, Kuwait. Al Ozairi and colleagues compared 250 people and found 12 month weight loss of 10.9% on tirzepatide, 9.9% on semaglutide and 7.1% on liraglutide, noting that weight loss "appeared less" than in people without diabetes.

A 2026 meta-analysis by Soliman and colleagues pooled six observational studies with 248 adults and found an average weight reduction of 9.9 kg and an HbA1c reduction of 0.61% at 6 months, while cautioning that overlapping patient groups limit the evidence. A similar gap between people with and without diabetes appears in type 2 diabetes, as our article on tirzepatide weight loss with type 2 diabetes explains.

How much does tirzepatide lower insulin needs in type 1 diabetes?

Tirzepatide lowered total daily insulin by roughly a quarter to a third across the published type 1 diabetes studies. The randomized trial found a 35.1% relative reduction versus placebo and the Mayo Clinic cohort a 31.6% reduction, while the meta-analysis found an average drop of 23.73 IU/day at 6 months, split between basal insulin (8.71 IU/day) and bolus insulin (15.02 IU/day).

Most of the change in insulin needs arrives in the first months of treatment. In the Mayo Clinic cohort the steepest decline came during the first 6 months, and a study by Karakus and colleagues of 11 adults using the Tandem Control-IQ automated insulin delivery (AID) system found that most of the drop happened within 2 months, with time in range rising by 7% and no increase in time below 70 mg/dl. The authors suggested cutting total daily insulin by 25% at the start for AID users with an A1c below 7.5%, but a pilot study of 11 people is not a guideline, so insulin changes belong with the clinician who manages a person's diabetes.

Does tirzepatide raise the risk of low blood sugar in type 1 diabetes?

Tirzepatide can raise the risk of low blood sugar in type 1 diabetes when insulin doses are not adjusted. Both the Zepbound and Mounjaro labels warn that using tirzepatide with insulin "may increase the risk of hypoglycemia, including severe hypoglycemia," and that reducing the insulin dose may be necessary.

The Mayo Clinic, Colorado and Kuwait cohorts reported no rise in severe hypoglycemia, but a 2026 survey by Akturk and colleagues of 230 adults at the Barbara Davis Center found symptomatic hypoglycemia reported by 29% of people on tirzepatide versus 13.4% on semaglutide. When appetite drops and meals shrink, a mealtime bolus sized for the old eating pattern can overshoot. Our article on low blood sugar on tirzepatide explains the mechanism in more detail, and our continuous glucose monitor guide covers what sensor data can show.

Can tirzepatide cause diabetic ketoacidosis in type 1 diabetes?

Diabetic ketoacidosis has been reported in people with type 1 diabetes taking tirzepatide, although the cohort studies did not report DKA events. DKA develops when the body lacks enough insulin and breaks down fat into acidic ketones, and cutting insulin too far or vomiting and eating very little can tip that balance.

A 2026 case report by Malik and colleagues described a 41 year old woman who developed severe euglycemic DKA, requiring intubation, after starting tirzepatide while also taking the SGLT2 inhibitor empagliflozin with insulin. Her glucose was only 190 to 200 mg/dL, which is why this form of DKA is easy to miss. A single case cannot show how often DKA occurs, but it illustrates why basal insulin should not be stopped and why vomiting in type 1 diabetes is a reason to check ketones.

Does tirzepatide affect diabetic eye disease in type 1 diabetes?

Early data suggest that tirzepatide does not change the rate of new diabetic retinopathy in type 1 diabetes, although a rapid drop in HbA1c may matter. A 2026 chart review by Polsky and colleagues followed 106 tirzepatide users and 85 controls, and among the participants assessed for new retinopathy, it developed in 10 of 39 tirzepatide users (25.6%) and 7 of 24 controls (29.2%). Across both groups, people whose HbA1c fell by 0.5% or more within 6 months developed retinopathy more often (39.3% versus 17.1%), so people with existing retinopathy should keep up regular eye exams, as our article on tirzepatide and eye health explains.

Who might consider tirzepatide with type 1 diabetes?

The studies so far enrolled adults with type 1 diabetes who also had overweight or obesity, many of them using sensors and insulin pumps, and no data support tirzepatide in lean adults with type 1 diabetes. Adults in this group who are interested should raise it with their endocrinologist, who can plan insulin reductions, ketone checks and a sick day plan before the first injection.

What research is still coming?

The TZP-T1D trial in Sydney (NCT06180616) plans to randomize 60 adults aged 18 to 70 with a BMI of 27 or more to tirzepatide or placebo for 32 weeks. Until results arrive, long term safety and the best insulin adjustment strategy remain open questions.

Frequently asked questions

A note for readers with type 1 diabetes. Aurelius does not manage insulin therapy, so anyone with type 1 diabetes should talk with their endocrinologist before considering any GLP-1 medicine.