No GLP-1 drug is approved for type 1 diabetes in the US. The question keeps being asked because people with type 1 diabetes increasingly live with excess weight too, and because a decade of trials has shown these drugs can lower weight and insulin needs when added to insulin. Those trials also found the reason no approval followed: more low blood sugars and more ketosis. A new round is about to report — Eli Lilly's first phase 3 trials of tirzepatide in type 1 diabetes list November 2026 as their primary completion date.
This page is the trial record and a registry count, read on 26 October 2026. What the labels themselves say about type 1 diabetes — and how that wording has changed since 2017 — is set out on our page is a GLP-1 drug insulin?; it is not repeated here.
Why the question is different in type 1 diabetes
In type 2 diabetes, GLP-1 drugs work partly by prompting the pancreas to release more insulin after a meal. In type 1 diabetes that insulin-making capacity is largely gone, so the drug's benefit has to come from its other actions — slowing the stomach, lowering appetite and suppressing glucagon. That is why the trials below measure weight and insulin dose as much as HbA1c, and why the main safety measures are hypoglycaemia and ketosis rather than nausea. How the drugs act on those pathways in general is on our how GLP-1 drugs work page.
The liraglutide trials: the programme that stopped
Novo Nordisk ran the only large industry programme so far, testing liraglutide (the molecule in Victoza and Saxenda) on top of insulin. Both trials were published in Diabetes Care in October 2016.
| Trial | People | Length | HbA1c vs placebo (1.8 mg) | Weight vs placebo (1.8 mg) | Safety signal |
|---|---|---|---|---|---|
| ADJUNCT ONE (NCT01836523) | 1,398 | 52 weeks, treat-to-target insulin | -0.20 points | -4.9 kg | Symptomatic hypoglycaemia rate ratio 1.31; hyperglycaemia with ketosis rate ratio 2.22 |
| ADJUNCT TWO (NCT02098395) | 835 | 26 weeks, insulin capped | -0.34 points* | -4.9 kg* | Hypoglycaemia higher on 1.2 mg; ketosis 0.5 vs 0.1 events per patient-year on 1.8 mg |
*ADJUNCT TWO reports changes from baseline: HbA1c -0.33 on 1.8 mg against +0.01 on placebo, weight -5.1 kg against -0.2 kg. The differences are glp1ledger's subtraction.
ADJUNCT ONE's authors concluded that the benefits were "accompanied by increased rates of symptomatic hypoglycemia and hyperglycemia with ketosis, thereby limiting clinical use in this group." A 0.2-point HbA1c difference is small next to the falls the same drug's type 2 diabetes trials report. Novo did not file for a type 1 indication.
Semaglutide: small trials, mostly with insulin pumps
The next wave came from academic centres and patient charities rather than drug makers, and most of it pairs semaglutide with automated insulin delivery — pumps that adjust insulin from a glucose sensor every few minutes, which should in principle absorb some of the hypoglycaemia risk.
| Trial | Who | Design | Main result |
|---|---|---|---|
| ADJUST-T1D (NCT05537233), NEJM Evidence 2025 | 72 adults, BMI ≥30, on automated insulin delivery | Semaglutide up to 1 mg vs placebo, 26 weeks | Composite target (time in range >70%, time below range <4%, weight loss ≥5%) reached by 36% vs 0%; HbA1c -0.3 points, weight -8.8 kg vs placebo; two severe hypoglycaemia events in each group; no diabetic ketoacidosis |
| McGill crossover (NCT05205928), Nature Medicine 2025 | 28 randomised, 24 completed | Semaglutide vs placebo with automated insulin delivery | Time in range +4.8 points; no increase in time below range; two episodes of recurrent euglycaemic ketosis without acidosis on semaglutide |
ADJUST-T1D was funded by Breakthrough T1D, the US type 1 diabetes charity, not by Novo Nordisk. A phase 3 trial of semaglutide plus dapagliflozin plus insulin ("Triple Therapy for Type 1 Diabetes", TTT1) published its design in 2026: a revised target of 82 participants, HbA1c above target at entry, and hypoglycaemia and ketosis as the safety outcomes. No result has been published.
Tirzepatide: one small trial, and Lilly's phase 3
The first randomised trial of tirzepatide in type 1 diabetes was an investigator-led study from Sydney, published in Diabetes Care in January 2026: 24 adults with type 1 diabetes and a BMI over 30, 12 weeks, tirzepatide 2.5 mg then 5 mg against placebo.
- Weight: -10.3 kg against -0.7 kg, a difference of 8.7 kg (8.8%).
- Insulin: total daily dose down 24.2 units against 0.3 — a 35% difference.
- HbA1c: -0.4 points against placebo, at the edge of significance (p=0.05).
- The authors report no significant adverse events in either group.
Twenty-four people for twelve weeks at low doses cannot say much about hypoglycaemia or ketosis. The trials that can are Lilly's:
| Trial | Registry | Planned size | Primary outcome | Started | Primary completion (est.) |
|---|---|---|---|---|---|
| SURPASS-T1D-1 | NCT06914895 | 905 | HbA1c change at 40 weeks vs placebo | April 2025 | November 2026 |
| SURPASS-T1D-2 | NCT06962280 | 465 | HbA1c change at 40 weeks vs placebo, plus long-term safety | May 2025 | November 2026 |
Both enrol adults with type 1 diabetes and obesity or overweight and are listed as active, not recruiting. In the registry census below they are the first drug-maker phase 3 trials of a GLP-1-based drug in type 1 diabetes since ADJUNCT TWO finished in 2015, and at about 1,370 people combined they are about the size of ADJUNCT ONE. "Primary completion" is when the last person reaches the main measurement; results usually follow months later.
The registry, counted
How much of the type 1 literature is finished, and how much is reported? glp1ledger searched ClinicalTrials.gov on 26 October 2026 for interventional studies naming type 1 diabetes and each drug, then kept only records whose conditions or title actually name type 1 diabetes (the registry's search also matches general "diabetes" records).
| Drug | Type 1 studies | Phase 3 | With results posted | Active or recruiting |
|---|---|---|---|---|
| Liraglutide | 37 | 14 | 13 | 1 |
| Semaglutide | 19 | 8 | 1 | 13 |
| Exenatide | 17 | 3 | 7 | 1 |
| Tirzepatide | 9 | 4 | 0 | 8 |
| Dulaglutide | 3 | 0 | 0 | 2 |
The shape is clear. Liraglutide's work is mostly finished and reported; semaglutide's and tirzepatide's is mostly still running, and only one semaglutide study in type 1 diabetes has posted results to the registry. Several "phase 3" labels belong to small academic trials of 30–120 people; only Novo's two liraglutide trials and Lilly's two tirzepatide trials are industry programmes of registration size, and one 2,000-person Danish trial (NCT06082063) tests a whole package of heart-risk treatments in which semaglutide is one part.
What the trials have not settled
- Ketoacidosis risk at scale. Ketosis appeared in ADJUNCT ONE and in the McGill crossover; no trial large enough to count diabetic ketoacidosis reliably has reported for semaglutide or tirzepatide.
- Long-term glucose benefit. The HbA1c gains so far are small — 0.2 to 0.4 points.
- Children and adolescents. Almost all of the trials are in adults.
- Whether any company will file. Lilly's trials are the first that could support an application; nothing has been filed.
Insulin doses in type 1 diabetes change with any drug that alters appetite or stomach emptying, and changing them is work for the person's diabetes team, not something a trial table can settle. Questions about off-label use belong there too. The approved uses in type 2 diabetes are on our Ozempic for type 2 diabetes and Mounjaro for type 2 diabetes pages, and the related question of the stage before type 2 is on GLP-1 for prediabetes.
Sources
- Mathieu C et al. "Efficacy and Safety of Liraglutide Added to Insulin Treatment in Type 1 Diabetes: The ADJUNCT ONE Treat-To-Target Randomized Trial." Diabetes Care 2016;39(10):1702-10, PubMed 27506222. Read 2026-10-26.
- Ahrén B et al. "Efficacy and Safety of Liraglutide Added to Capped Insulin Treatment in Subjects With Type 1 Diabetes: The ADJUNCT TWO Randomized Trial." Diabetes Care 2016;39(10):1693-701, PubMed 27493132. Read 2026-10-26.
- Shah VN et al. "Semaglutide in Adults with Type 1 Diabetes and Obesity." NEJM Evidence 2025;4(8), PubMed 40550013. Read 2026-10-26.
- Pasqua MR et al. "Subcutaneous weekly semaglutide with automated insulin delivery in type 1 diabetes: a double-blind, randomized, crossover trial." Nat Med 2025;31(4):1239-1245, PubMed 39794615. Read 2026-10-26.
- Snaith JR et al. "Tirzepatide in Adults With Type 1 Diabetes: A Phase 2 Randomized Placebo-Controlled Clinical Trial." Diabetes Care 2026;49(1):161-170, PubMed 41264593. Read 2026-10-26.
- "Insulin, Semaglutide and Dapagliflozin in Adults With Type 1 Diabetes: Design and Methods of Triple Therapy for Type 1 Diabetes (TTT1)." Diabetes Obes Metab 2026, PubMed 42473259. Read 2026-10-26.
- WEGOVY prescribing information, DailyMed set ee06186f-2aa3-4990-a760-757579d8f77b, version 19, effective 18 June 2026, dailymed.nlm.nih.gov. Read 2026-10-26.
- ClinicalTrials.gov API v2: records NCT06914895, NCT06962280, NCT05537233, NCT05205928, NCT01836523, NCT02098395, NCT06082063, and the condition-and-intervention census above, clinicaltrials.gov. Read 2026-10-26.
- PubMed search for randomised controlled trials with liraglutide, semaglutide, tirzepatide or dulaglutide and "type 1 diabetes" in the title: 36 records on 26 October 2026.