Tirzepatide Is Associated With Improved Metabolic Outcomes in People With Type 1 Diabetes and Overweight or Obesity: A Retrospective Cohort Study.

AIMS: To evaluate the effect of tirzepatide on body weight, glycaemic control, insulin requirements, continuous glucose monitoring (CGM) metrics and cardiorenal parameters in adults with Type 1 diabetes (T1D) and overweight or obesity. MATERIALS AND METHODS: In this retrospective matched cohort study, adults with T1D, BMI ≥ 27 kg/m, CGM use and available baseline and follow-up electronic medical record data from Royal North Shore Hospital and the Northern Sydney Endocrine Centre between 2020 and 2025 were included. Twenty-three adults treated with tirzepatide were identified and propensity score-matched to 23 control participants. Primary outcomes included changes in percentage change in body weight, HbA1c, total daily insulin dose and CGM-derived metrics from baseline to follow-up. Exploratory outcomes included changes in blood pressure and biochemical markers. RESULTS: Mean follow-up duration in the tirzepatide and control groups were 28 and 31 weeks, respectively. The most common dose of tirzepatide was 5 mg/week (52.2% participants). Compared with controls, tirzepatide was associated with greater reductions in body weight (-10.01% ± 4.74% vs. +0.69% ± 3.77%, adj-p < 0.0001) and total daily insulin dose (-21.82 ± 16.30 vs. +5.62 ± 11.63 U/day; adj-p = 0.002). From baseline to end-of-study, tirzepatide was associated with a reduction in glucose management indicator, glucose SD and daily carbohydrate intake. Other CGM, blood pressure, lipid, hepatic and renal outcomes did not differ. CONCLUSIONS: In adults with T1D and overweight or obesity, adjunctive tirzepatide treatment was associated with clinically meaningful reductions in percentage body weight and insulin requirements. Larger prospective studies are needed to confirm efficacy, ensure safety and assess broader cardiometabolic effects.