This research study is testing whether a weekly medication called tirzepatide can help adults with type 1 diabetes use their insulin pump more easily, specifically by reducing or eliminating the need to count carbohydrates at meals.

People with type 1 diabetes must take insulin for life, and even with advanced insulin pumps and continuous glucose monitors, many still struggle to keep blood sugar within the target range. One of the biggest challenges is carbohydrate counting, which requires estimating the amount of carbohydrates in every meal to give the correct insulin dose.

Tirzepatide is a medication currently approved for type 2 diabetes and weight management. Early research suggests it may also help people with type 1 diabetes by lowering appetite, slowing digestion, reducing insulin needs, and smoothing after-meal blood sugar rises.

This study will include 105 adults with type 1 diabetes at centers in Canada and Switzerland. Everyone will use the Tandem Control-IQ insulin pump with a Dexcom G7 continuous glucose monitor. Participants are randomly assigned to one of two groups:

Tirzepatide group:

Participants receive weekly tirzepatide injections. After the dose is gradually increased over 12 weeks, they will eventually try using their insulin pump without entering carbohydrate amounts at meals.

Control group:

Participants continue their usual therapy and keep counting carbohydrates for their mealtime insulin doses.

The main goal of the study is to learn whether people taking tirzepatide can safely maintain good blood sugar control without counting carbs, compared with standard care. All participants will attend several clinic visits and share their glucose, insulin, and health data throughout the 32-week trial. Some centers will also conduct heart/fitness, or body-composition tests.

As with any medication, tirzepatide may cause side effects such as nausea, vomiting, diarrhea, or decreased appetite. Rare but serious risks like gallbladder disease or pancreatitis are also monitored. Pregnancy must be avoided during the trial.

Overall, this study aims to understand whether adding tirzepatide to automated insulin delivery can simplify diabetes management, reduce burden, and maintain safe and effective glucose control for adults living with type 1 diabetes.

Current diabetes technology, including hybrid automated insulin delivery systems like the Tandem Control-IQ paired with the Dexcom G7 continuous glucose monitor, improves glucose control but still relies heavily on patients entering carbohydrate amounts before eating, a task that is difficult, error-prone, and often stressful.

Tirzepatide, which is approved for type 2 diabetes and weight management, works by slowing digestion, lowering appetite, reducing insulin requirements, and improving after-meal glucose spikes, and early evidence suggests it may offer similar benefits in type 1 diabetes. This study is designed to determine whether adding once-weekly tirzepatide injections to a commercially available automated insulin delivery system can make diabetes management easier for adults with type 1, particularly by reducing or eliminating the need to count carbohydrates at meals.

In this 32-week trial, 105 adults will be randomly assigned to receive tirzepatide or no tirzepatide while all participants use the Control-IQ system. Those receiving tirzepatide will gradually increase their dose over 12 weeks, continue counting carbohydrates until week 26, and then stop announcing meals entirely for the final 6 weeks, while the control group will count carbohydrates throughout.

Across the study, participants will attend scheduled clinic visits, complete remote follow-ups, undergo laboratory tests, and, depending on the site, may complete heart function tests, body-composition scans, fitness testing, or gastric emptying assessments. Researchers will compare glucose control, insulin needs, weight, metabolic markers, meal patterns, and patient-reported outcomes between groups, with the primary goal of determining whether glucose management without carbohydrate counting is not worse than (non-inferior to) standard carbohydrate counting.

The study also closely monitors safety, as tirzepatide can cause nausea, vomiting, diarrhea, decreased appetite, and rare complications such as gallbladder disease or pancreatitis. Overall, this research aims to learn whether combining tirzepatide with automated insulin delivery can safely simplify diabetes management, reduce treatment burden, and improve metabolic outcomes for adults living with type 1 diabetes.

Inclusion Criteria:

• Age ≥ 18 years.
• Clinical diagnosis of type 1 diabetes for ≥ 1 year, per investigator judgment (confirmatory C-peptide and autoantibodies not required).
• A BMI ≥ 27 kg/m2.
• HbA1c > 6.5%, and < 12%.
• Current therapy: multiple daily injections or insulin pump.
• Willingness to use Tandem Control IQ insulin pump system with the use of rapid or ultra rapid-acting insulins compatible with Tandem Control-IQ pump (e.g. Fiasp is not compatible)
• Active carbohydrate counting for prandial insulin dosing.
• Individuals of childbearing potential must be using or agree to use an effective birth-control method. Childbearing potential refers to participants of the female sex post-menarche who have not reached menopause and who do not have a medical condition causing sterility (e.g., hysterectomy). Post-menopausal state refers to the absence of menses for 12 months without any alternative cause.

Exclusion Criteria:

• Use of GLP1-RAs within the last four weeks.
• Use of antihyperglycemic agents other than insulin or metformin within the last 2 weeks.
• Planned or ongoing pregnancy.
• Breastfeeding.
• Severe hypoglycemia requiring hospitalization in the past 2 months. Severe hypoglycemia is defined as requiring the assistance of another person, due to altered consciousness, to administer carbohydrates, glucagon, or other resuscitative actions.
• Diabetic ketoacidosis within the last 2 months.
• History of acute or chronic pancreatitis.
• Personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2.
• Severe renal impairment with eGFR <30 mL/min/1.73 m2 (CKD-EPI), measured within the last four months.
• Clinically significant proliferative diabetic retinopathy or gastroparesis, as per the judgment of the investigator.
• Current or ≤ 1 month use of supraphysiological doses of oral or intravenous glucocorticoids.
• History of bariatric surgery within the last 6 months.
• Medical or psychiatric illness likely to interfere with participation (e.g. cirrhosis, active cancer, decompensated schizophrenia), per investigator judgment.
• Inability or unwillingness to comply with safe diabetes management practices, in the view of the investigator.
• Any safety concern that, in the investigator's judgment, precludes participation.

De-identified individual participant data may be shared with qualified researchers after completion of the trial and publication of the primary results. Shared data may include de-identified demographic variables, glucose and insulin delivery data, laboratory results, questionnaire scores, and device-based assessments collected during the study. All data will be reviewed to minimize re-identification risk in accordance with Canadian and Swiss privacy regulations. Researchers must submit a scientifically valid proposal and sign a data use agreement. Requests will be reviewed by the study team, and approved data will be provided through a secure transfer process.

IPD will be made available beginning 12 months after publication of the primary results and for a period of five years thereafter.

Researchers must submit a scientifically valid proposal and sign a data use agreement.