GLP-1 for Type 1 Diabetes: What the Research Actually Shows
No GLP-1 drug is FDA-approved for type 1 diabetes. One small randomized trial found 36% of adults on semaglutide hit a combined glucose-and-weight goal versus 0% on placebo, with weight 8.8 kg lower than placebo at 26 weeks.
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No GLP-1 medication — Ozempic, Wegovy, or Mounjaro — is approved by the FDA for type 1 diabetes. Every diabetes-related indication in their prescribing information covers type 2 diabetes only [1][2][3]. So any use in type 1 diabetes is off-label, decided case by case between a patient and their diabetes care team.
The research base is real but thin. One randomized controlled trial, ADJUST-T1D, tested once-weekly semaglutide in 72 adults with type 1 diabetes and obesity, all using automated insulin delivery (AID) systems. It found meaningful benefits: 36% of the semaglutide group met a combined glucose-and-weight goal versus 0% of the placebo group, with body weight 8.8 kg lower than placebo after 26 weeks [5]. A separate real-world study of 142 adults with type 1 diabetes on tirzepatide (Mounjaro’s active drug) found an HbA1c reduction of 6.5 mmol/mol (0.6%) and a weight reduction of 13.4 kg versus matched controls over about a year [8]. Both studies are small or observational, and neither changes the approval status.
Is any GLP-1 drug approved for type 1 diabetes?
No. Ozempic (semaglutide) is approved for glycemic control in adults with type 2 diabetes, for reducing major adverse cardiovascular events in adults with type 2 diabetes and established cardiovascular disease, and for reducing sustained eGFR decline, end-stage kidney disease, and cardiovascular death in adults with type 2 diabetes and chronic kidney disease [2]. Mounjaro (tirzepatide) is approved for glycemic control in adults and pediatric patients 10 years and older with type 2 diabetes, and for cardiovascular risk reduction in adults with type 2 diabetes at high risk [3].
Wegovy (semaglutide) comes in two forms with different indications. Wegovy injection is approved, alongside a reduced calorie diet and increased physical activity, for reducing the risk of major adverse cardiovascular events, for reducing excess body weight and maintaining that reduction in adults and pediatric patients 12 and older with obesity, for the same weight reduction in adults with overweight plus at least one weight-related comorbid condition, and for treating noncirrhotic MASH with F2–F3 fibrosis under accelerated approval [1]. Wegovy tablets are approved only for reducing the risk of major adverse cardiovascular events in adults with established cardiovascular disease and either obesity or overweight [1].
None of the three labels lists type 1 diabetes as an indication [1][2][3]. Ozempic and Wegovy are GLP-1 receptor agonists; Mounjaro is a GIP and GLP-1 receptor agonist [1][2][3]. The labels were revised in 06/2026 (Wegovy), 05/2026 (Ozempic), and 8/2026 (Mounjaro) [1][2][3].
What did the ADJUST-T1D trial test?
ADJUST-T1D was a 26-week, double-blind randomized trial that enrolled 72 adults with type 1 diabetes and a BMI of 30 or higher, all using an automated insulin delivery system, randomized 1:1 to once-weekly semaglutide up to 1 mg or placebo [5]. The dose studied was up to 1 mg once weekly [5][6] — lower than the 2.4 mg usual maintenance dose listed for Wegovy injection in its prescribing information [1].
The trial was funded by Breakthrough T1D, with Novo Nordisk supplying the drug and matched placebo at no cost; it is registered on ClinicalTrials.gov as NCT05537233 [5]. It was published in NEJM Evidence, volume 4, number 8, online on June 23, 2025, and in the issue dated July 22, 2025 [5].
The primary endpoint was a composite: participants had to hit all three of CGM time in range (70–180 mg/dL) above 70%, time below 70 mg/dL under 4%, and at least a 5% weight reduction [5].
What were the ADJUST-T1D results?
The semaglutide group did better on the composite endpoint: 36% versus 0% for placebo, a between-group difference of 36 percentage points (95% CI 20.6 to 52.2, P<0.001) [5][6]. On individual measures, the least-squares mean difference versus placebo at week 26 was −0.3 percentage points for HbA1c (95% CI −0.6 to −0.05), +8.8 percentage points for time in range 70–180 mg/dL (95% CI 3.9 to 13.7), and −8.8 kg for body weight (95% CI −10.6 to −7.0) [5].
Two numbers deserve a careful read. The −8.8 kg figure is the difference between the semaglutide and placebo groups, not what any individual lost [5]. And the trial was small — 72 people — with every participant on an AID system, so the results do not transfer to people using multiple daily injections or non-automated pumps [5].
On safety, there were two severe hypoglycemia events in each group, and no diabetic ketoacidosis was reported [5]. A post hoc analysis found roughly a 30% reduction in insulin requirements versus placebo [6]. A separate post hoc analysis of insulin dosing from the same trial was published in Diabetes Care, but its detailed figures are not in the material reviewed here [13].
| Measure (week 26, vs placebo) | Result | 95% CI |
|---|---|---|
| Composite endpoint achieved | 36% (semaglutide) vs 0% (placebo); between-group difference 36 percentage points | 20.6 to 52.2 percentage points (CI for the between-group difference) |
| HbA1c | −0.3 percentage points | −0.6 to −0.05 |
| Time in range 70–180 mg/dL | +8.8 percentage points | 3.9 to 13.7 |
| Body weight | −8.8 kg | −10.6 to −7.0 |
What happens when semaglutide is stopped?
A 12-week extension of ADJUST-T1D followed 16 participants who discontinued semaglutide and 22 prior-placebo participants who took no GLP-1 during follow-up [6]. Those who stopped semaglutide saw time in range fall by a median of 3.6%, while the comparison group rose 1.5% (adjusted p=0.044) [6]. Glucose variability worsened: standard deviation rose 6.0 versus 1.2 mg/dL, and coefficient of variation rose 3.1% versus 1.1% (both adjusted p=0.044) [6]. Time above 180 mg/dL increased numerically but did not stay significant after adjustment (adjusted p=0.064), and there were no significant between-group differences in hypoglycemia metrics [6].
The authors concluded that the glycemic benefits achieved during treatment may not be fully sustained after withdrawal [6]. That fits a pattern seen in other populations: a 4-week off-treatment analysis of SURPASS-1 found HbA1c rose about 0.2% after tirzepatide stopped; a meta-analysis found rebound HbA1c increases of 0.25% in obesity and 0.65% in type 2 diabetes; and the STEP 1 extension found cardiometabolic measures reverted toward baseline one year after semaglutide withdrawal [6]. In earlier type 1 diabetes pump data, semaglutide withdrawal raised insulin requirements, mainly bolus insulin, with a numerical decrease in time in range [6]. The extension analysis was published in Diabetes, Obesity and Metabolism, first published August 31, 2026 [6].
What does real-world tirzepatide data show in type 1 diabetes?
A retrospective cohort study from Sheffield Teaching Hospitals and the University of Sheffield compared 142 adults with type 1 diabetes and BMI of 30 kg/m² or higher who started tirzepatide against 50 age-, sex-, and BMI-matched controls, with a median follow-up of 365 days [8]. At baseline, participants had a mean age of 42.8 years, BMI 37.4 kg/m², HbA1c 64.3 mmol/mol, and 32% were male [8]. The median tirzepatide dose was 5 mg weekly [8].
Compared with controls, the tirzepatide group had mean reductions of 6.5 mmol/mol in HbA1c (95% CI 3.8–9.1), equal to 0.6% (0.4–0.8), p<0.001; 13.4 kg in weight (95% CI 11.0–15.8), p<0.001; and 29.9 units in total daily insulin dose (95% CI 16.9–42.9), p<0.001 [8]. Systolic blood pressure fell 12.6 mmHg (p<0.001) and diastolic fell 4.1 mmHg (p=0.034); total cholesterol fell 0.8 mmol/L, non-HDL cholesterol 0.6 mmol/L, and triglycerides 0.7 mmol/L (all p<0.001) [8].
Despite common side effects, 89.4% were still on tirzepatide at one year, and there was no between-group difference in severe hypoglycemia, ketoacidosis, or hospitalization rates [8]. The 13.4 kg figure is a between-group difference versus controls, not a prediction for any individual. The study was published in Diabetes, Obesity and Metabolism, volume 28, issue 10, pages 8836–8846, first published July 6, 2026 [8].
Is there any nationwide or registry evidence?
A Danish nationwide cohort study of semaglutide effectiveness and safety in type 1 diabetes, covering 2018–2024, was published in The Lancet Regional Health – Europe in 2026 [7]. Its specific results are not in the material reviewed here, so no figures from it can be reported.
What do the labels say about insulin and hypoglycemia?
All three labels warn that using these drugs together with insulin or an insulin secretagogue can increase the risk of hypoglycemia, including severe hypoglycemia, and that reducing the insulin dose may be necessary — a decision for a prescriber [1][2][3]. The Wegovy label adds that patients with diabetes should have blood glucose monitored before starting and during treatment, and that patients should be educated on the signs and symptoms of hypoglycemia [1]. The Wegovy label also states that using it with other semaglutide products or any other GLP-1 receptor agonist is not recommended [1].
The documented insulin reductions in type 1 diabetes studies — about 30% in the ADJUST-T1D post hoc analysis and 29.9 units per day in the Sheffield cohort — underline why insulin adjustments on these drugs belong with a diabetes care team, not done alone [6][8].
What about diabetic retinopathy?
The Ozempic label reports that diabetic retinopathy complications were seen in a clinical trial and that patients with a history of diabetic retinopathy should be monitored [2]. The Wegovy label carries a similar warning about retinopathy complications reported with semaglutide in patients with type 2 diabetes [1]. The Mounjaro label, in a section added 08/2026, instructs monitoring patients with a history of diabetic retinopathy for progression [3].
A 2026 report by Polsky et al. in Diabetes Technology & Therapeutics examined incident diabetic retinopathy after one year of adjunctive tirzepatide in adults with type 1 diabetes; only its title is available in the material reviewed here, so its findings cannot be characterized [10].
What about DKA and other class risks?
No diabetic ketoacidosis was reported in ADJUST-T1D, and the Sheffield tirzepatide cohort showed no between-group difference in ketoacidosis rates [5][8]. That is reassuring but limited: one trial had 72 participants, and the cohort study was observational [5][8].
Beyond that, the labels carry class-wide warnings. Semaglutide and tirzepatide are not recommended in patients with severe gastroparesis [1][2][3]. All three drugs delay gastric emptying and may affect absorption of oral medications [1][2][3]. Other listed warnings include acute pancreatitis, acute gallbladder disease, acute kidney injury from volume depletion, pulmonary aspiration of stomach contents during general anesthesia or deep sedation, and hypersensitivity reactions including anaphylaxis [1][2][3]. All three carry a boxed warning about thyroid C-cell tumors in rodents and are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2 [1][2][3].
The most common adverse reactions reported at 5% or more include nausea, vomiting, diarrhea, constipation, and abdominal pain; the Mounjaro label adds decreased appetite and dyspepsia [2][3]. The labels also state never to share pens between patients, even with a needle change [1][2][3].
What research is still underway?
TTT1 (Triple Therapy for Type 1 Diabetes) is an international phase 3 trial of insulin plus semaglutide plus dapagliflozin in adults with type 1 diabetes; its design and methods paper appeared in Diabetes, Obesity and Metabolism in 2026 [9]. A 2026 study in Diabetes/Metabolism Research and Reviews examined weight-loss-dependent body composition and bone health changes in people with obesity and type 1 diabetes treated with liraglutide, semaglutide, or tirzepatide — title only, no verified results [11]. Combination GLP-1 receptor agonist plus SGLT inhibitor use in type 1 diabetes is also discussed in 2026 review literature [5].
What about adolescents with type 1 diabetes?
Evidence in adolescents is minimal. A 2026 case report in Pediatrics described the effects of semaglutide on weight and insulin requirements in two adolescents with type 1 diabetes — a sample of two, which cannot establish anything general [12]. On the label side, Wegovy’s weight indication covers pediatric patients 12 and older with obesity, while Mounjaro’s pediatric indication is for type 2 diabetes in patients 10 years and older, with a maximum dose of 10 mg weekly [1][3].
What should someone with type 1 diabetes ask their care team?
A few questions follow directly from the evidence. First, whether their insulin delivery setup matches the studied population — the randomized evidence comes only from AID users, so people on injections or non-automated pumps should ask how that limits what the data can tell them [5]. Second, how insulin doses will be handled, given the reductions documented in both the trial and the real-world cohort [6][8]. Third, eye monitoring, since all three labels call for monitoring patients with a history of diabetic retinopathy [1][2][3].
It is also worth asking what to expect if treatment stops, since the extension study found time in range declined and glucose variability increased after withdrawal [6]. Anyone planning surgery or procedures should tell their clinicians, because of the aspiration warning on all three labels [1][2][3]. And for anyone who may become pregnant, the Ozempic and Wegovy labels instruct discontinuing semaglutide at least 2 months before a planned pregnancy [1][2].
Sources
- Novo Nordisk. Wegovy (semaglutide) injection prescribing information.
- Novo Nordisk. Ozempic (semaglutide) injection prescribing information.
- Eli Lilly and Company. Mounjaro (tirzepatide) injection prescribing information.
- ClinicalTrials.gov. Clinical study record NCT06075667.
- NEJM Evidence. Semaglutide in adults with type 1 diabetes and obesity.
- Diabetes, Obesity and Metabolism. Glycaemic changes after semaglutide discontinuation in adults with type 1 diabetes using automated insulin delivery: analysis of the ADJUST-T1D extension study.
- The Lancet Regional Health – Europe. Effectiveness and safety of semaglutide in type 1 diabetes: a Danish nationwide cohort study (2018–2024).
- Diabetes, Obesity and Metabolism. Real-world effectiveness and safety of tirzepatide in type 1 diabetes and obesity: impact on glycaemia, weight, and cardiometabolic risk markers. 2026.
- Diabetes, Obesity and Metabolism. Insulin, semaglutide and dapagliflozin in adults with type 1 diabetes: design and methods of Triple Therapy for Type 1 Diabetes (TTT1)—an international phase 3 clinical trial. 2026.
- Diabetes Technology & Therapeutics. Incident diabetic retinopathy after adjunctive tirzepatide treatment for 1 year in adults with type 1 diabetes. 2026.
- Diabetes/Metabolism Research and Reviews. Weight loss-dependent changes in body composition and bone health in people with obesity and type 1 diabetes treated with liraglutide, semaglutide, or tirzepatide. 2026.
- Pediatrics. Effects of semaglutide on weight and insulin requirements in two adolescents with type 1 diabetes.
- Diabetes Care. Effect of semaglutide on insulin dose reduction in adults with type 1 diabetes and obesity using automated insulin delivery systems: ADJUST-T1D post hoc analysis. May 2026.
- ClinicalTrials.gov. Clinical study record NCT06075667.
Frequently asked questions
Is any GLP-1 approved by the FDA for type 1 diabetes?
No. Ozempic, Wegovy, and Mounjaro have no type 1 diabetes indication in their prescribing information. Every diabetes indication listed covers type 2 diabetes only, so use in type 1 diabetes is off-label.
Does semaglutide cause ketoacidosis in type 1 diabetes?
No DKA was reported in the 72-person ADJUST-T1D trial, and a 142-person real-world tirzepatide cohort found no difference in ketoacidosis rates versus controls. Both studies are small or observational, so they cannot rule out risk.
How much weight do people with type 1 diabetes lose on these drugs?
In ADJUST-T1D, the semaglutide group weighed 8.8 kg less than placebo at 26 weeks. In the Sheffield cohort, tirzepatide users weighed 13.4 kg less than matched controls at one year. Both are between-group differences, not individual outcomes.
Does a GLP-1 lower HbA1c in type 1 diabetes, and by how much?
ADJUST-T1D found an HbA1c difference of −0.3 percentage points versus placebo at 26 weeks. The Sheffield tirzepatide cohort found a 6.5 mmol/mol (0.6%) reduction versus controls over about a year.
What dose of semaglutide was studied in type 1 diabetes?
ADJUST-T1D tested once-weekly semaglutide up to 1 mg in 72 adults with type 1 diabetes and obesity, all using automated insulin delivery. For comparison, the usual maintenance dose listed for Wegovy injection in its label is 2.4 mg once weekly.
How much were insulin doses reduced in the type 1 diabetes studies?
Large reductions were documented: about 30% in a post hoc ADJUST-T1D analysis and 29.9 units per day in the Sheffield tirzepatide cohort. The labels state reducing insulin may be necessary with concomitant use — a prescriber's decision.
What happens to glucose control after stopping the drug?
In a 12-week extension, those who stopped semaglutide lost 3.6% of time in range while the comparison group gained 1.5%, and glucose variability rose. The authors concluded glycemic benefits may not be fully sustained after withdrawal.
Is tirzepatide (Mounjaro) studied in type 1 diabetes?
Not in a randomized trial in the material reviewed here. The main evidence is a retrospective cohort of 142 adults with type 1 diabetes and obesity on tirzepatide versus 50 matched controls, which found improvements in HbA1c, weight, insulin dose, and blood pressure.
This article summarizes FDA labeling, published research and company information current as of September 14, 2026. It is not medical advice and does not replace a conversation with your own healthcare provider. How we research and verify.