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Efficacy and Safety of Tirzepatide Versus Placebo in Adults with Type 1 Diabetes and Obesity or Overweight: A Phase 3 Randomized Controlled Trial

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying Type 1 Diabetes in adults who are also overweight or have obesity. The treatment being tested is called tirzepatide (also known by its code name LY3298176), which is given as a solution for injection using a pre-filled pen. The purpose of the study is to see if tirzepatide can help control blood sugar levels better than a placebo.

Participants in the study will receive either tirzepatide or a placebo once a week. The study will last for about 40 weeks. During this time, the effects of tirzepatide on blood sugar levels will be closely monitored. The study aims to determine if tirzepatide is more effective than a placebo in managing blood sugar levels in people with Type 1 Diabetes.

This study is important for understanding how tirzepatide can help people with Type 1 Diabetes who are also dealing with being overweight or obese. The results could provide valuable insights into new treatment options for better managing blood sugar levels in these individuals.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and consent

    After agreeing to take part, you sign a consent form that explains the study in simple language.

    Your eligibility for the study is confirmed at this point.

  2. Step 2

    Baseline assessments

    A series of measurements are taken before any medication is given, including blood tests for hemoglobin a1c, weight, and other health checks.

    The results are recorded as the baseline values that will be compared with later results.

  3. Step 3

    Randomization

    You are assigned, by a computer system, to receive either tirzepatide or a matching placebo without knowing which one you receive.

  4. Step 4

    Injection training

    A study staff member shows you how to use the pre‑filled pen for a subcutaneous injection (injection under the skin).

    You practice the technique until you feel comfortable performing the injection yourself.

  5. Step 5

    Start of weekly injections

    You begin giving yourself an injection once each week.

    The medication is tirzepatide for those assigned to the active group, or a matching placebo for the control group.

    The exact dose is set by the study protocol and is delivered using the pre‑filled pen.

    This weekly schedule continues for the full study period, which lasts until week 40.

  6. Step 6

    Regular clinic visits

    You attend visits at the study site roughly every four weeks.

    During each visit, blood samples are taken to check hemoglobin a1c and other safety parameters.

    Any side effects or concerns are reviewed, and the study team confirms that the weekly injections are being taken as planned.

  7. Step 7

    Final assessment at week 40

    At the end of week 40, a comprehensive set of measurements is repeated, including the primary endpoint of change in hemoglobin a1c from the baseline value.

    The study medication is stopped after this final assessment.

  8. Step 8

    Study completion

    After the final visit, you are no longer required to follow the study schedule.

    The study team may discuss any further follow‑up that is needed for your health.

Who can join the trial?

5 criteria

  • Be at least 18 years old.
  • Have type 1 diabetes (a condition where the body does not produce insulin) and be using insulin therapy for at least one year.
  • Have a body weight that is classified as obesity (very high body weight) or overweight (higher than normal weight).
  • Have blood glucose levels (the amount of sugar in the blood) that fall within the range allowed by the study.
  • Be either male or female (any gender is accepted).

Who cannot join the trial?

3 criteria

  • Been hospitalized (had to stay in the hospital) two or more times because of very high blood sugar (hyperglycemia) in the past six months.
  • Had an emergency treatment (needed urgent medical help) for very low blood sugar (hypoglycemia) at least once in the past three months.
  • Are currently receiving or planning to receive treatment for diabetic eye disease (damage to the eyes caused by diabetes).
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Investigated drugs

Tirzepatide is a medication that is given as a solution for injection, using a pre‑filled pen that you place under the skin (subcutaneous use). In this study participants receive it once a week. The drug is being tested to see if it can improve blood sugar control and help reduce weight in adults who have type 1 diabetes and are overweight or obese. Researchers are looking at how well it works compared with a placebo and whether it is safe to use.

What is already known about the treatment

Tirzepatide - Tirzepatide is given as a liquid that you inject under the skin using a pre‑filled pen, usually once a week. It is an approved drug that has been studied in many clinical trials and is listed in the medical literature for diabetes and weight management. It is used to improve blood sugar control in diabetes and to help reduce body weight in people who are overweight or have obesity. The medicine works by activating two natural hormones (GIP and GLP‑1) that tell the pancreas to release insulin after meals and also reduce appetite, and it belongs to the class of dual GIP/GLP‑1 receptor agonist peptides.

Investigated diseases

  • Obesity

    A condition in which a person has an excessive amount of body fat, resulting in a weight that is higher than what is considered healthy. It usually develops slowly as a result of eating more calories than the body uses, causing fat to build up over time. The extra fat can increase gradually and may affect many parts of the body.

  • Type 1 Diabetes

    A condition where the pancreas stops producing insulin, the hormone that helps lower blood sugar. It often begins in childhood or early adulthood, and without insulin the blood sugar level rises because glucose cannot enter the cells. The high blood sugar persists and may worsen if the lack of insulin continues.

  • Overweight

    A state where a person's weight is higher than normal for their height but not as high as obesity. It results from regularly consuming more energy than the body burns, leading to a modest increase in body fat. This extra weight can build up slowly over months or years.

Trial detailsLast updated 14 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-519684-17-00Protocol codeI8F-MC-GPJAEstimated enrolment905 patientsSponsorEli Lilly & Co.

sourced from the EU Clinical Trials Register and site verification

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