Diabetes Care

Obesity in type 1 diabetes: Tirzepatide beats placebo for weight loss

December 26, 2025

Tirzepatide titrated to 5 mg/week led to improvements in weight, insulin use, and HbA1c, compared with placebo, in obese patients with type 1 diabetes, in this 12-week phase 2 RCT. No episodes of severe hypoglycemia or ketoacidosis occurred during the study. Although weight loss improves insulin sensitivity, the magnitude of reduction in insulin requirements adjusted for body weight led authors to speculate whether tirzepatide may have additional metabolic effects independent of weight loss.

• Study details: 22 adults with type 1 diabetes and BMI >30 kg/m² were randomized to weekly subcutaneous tirzepatide (2.5 mg x 4 weeks, then 5.0 mg x 8 weeks) vs. placebo.
• Weight loss. The tirzepatide group lost a mean of 10.3 kg, the placebo group lost a mean of 0.7 kg, for a difference of −8.7 kg (p<0.0001), equating to about 8.8% body weight loss over 12 weeks.
• HbA1c improved −0.4% with tirzepatide vs. placebo (p=0.05).
• Total daily insulin use dropped by 35.1% with tirzepatide vs. placebo (p=0.0002). In insulin pump users, reduced insulin requirements were seen as early was week 2.
• Adverse events. Non-serious GI adverse events were seen with tirzepatide. No significant adverse events occurred in either study arm.

Source:

Snaith JR, et al. (2026, January 1). Diabetes Care. Tirzepatide in Adults With Type 1 Diabetes: A Phase 2 Randomized Placebo-Controlled Clinical Trial. https://pubmed.ncbi.nlm.nih.gov/41264593/