This study is a planned 32‑week trial to see if tirzepatide, a drug that works on two gut hormone receptors, can help adults with type‑1 diabetes who are also overweight lose weight and improve blood‑sugar control. It will compare tirzepatide to a placebo while participants keep their usual insulin, measuring weight loss, HbA1c changes, insulin dose adjustments, and glucose‑monitoring metrics. No results are available yet, but the design shows how the drug might be tested in this group.

The increasing prevalence of overweight and obesity among individuals with type 1 diabetes (T1D) complicates glycaemic management and escalates insulin resistance, necessitating innovative therapeutic strategies. Tirzepatide, a dual agonist for glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide receptors, shows promise in managing weight and glycaemic control in type 2 diabetes but is unexplored in the context of T1D. This double-blind, placebo-controlled randomised trial will evaluate the efficacy of tirzepatide in adults with T1D and overweight/obesity over 32 weeks. 60 participants (aged 18-70 years) with a body mass index ≥27 kg/m² and HbA1c≤10% will be randomised 1:1 to receive either tirzepatide or a placebo, alongside standard insulin therapy. The primary outcome is the change in body weight (%). Secondary measures include change in HbA1c (%), proportion of body weight lost (>5%, >10%, >15% and >20%), changes in insulin dosage, time in range by continuous glucose monitoring (CGM) criteria and severity of comorbidities. Compliance, adverse events and medication interactions will be closely monitored, with adjustments made for tolerability. Patient-reported outcomes and experiences will be measured to capture the benefits of glycaemic management, weight management and quality of life. To compare the means of body weight reduction (%) between the tirzepatide and control groups, an independent samples t-test will be employed under the assumption that data are normally distributed. Secondary outcome measures will be analysed by Student's t-test. All data will be reported as group means with confidence intervals, with default statistical significance assumed at p<0.05. Ethical approval has been obtained from the Northern Sydney Local Health District's Human Research Ethics Committee (approval ID #2024/ETH00180). NCT06180616.