GLP-1s for Type 1 Diabetes: The Off-Label Evidence (Ozempic, Wegovy, Mounjaro, Zepbound)

GLP-1 receptor agonists — Ozempic, Wegovy, Mounjaro, Zepbound, Rybelsus, and Foundayo — are not FDA-approved for type 1 diabetes. Every prescription written for a T1D patient is off-label. The evidence base is thinner than for type 2 diabetes or obesity but is no longer empty: the two ADJUNCT liraglutide RCTs in ~2,000 T1D adults (Mathieu 2016 ADJUNCT ONE^[1], Ahrén 2016 ADJUNCT TWO^[2]), a recent Danish nationwide cohort of 1,517 T1D adults on semaglutide (Würtz Yazdanfard 2026^[6]), the Garg 2024 semaglutide pilot in overweight T1D^[4], a 2-year real-world CGM study (Al Hayek 2025^[5]), and a 2026 systematic review of tirzepatide T1D data (Acucella^[7]) all show consistent signals: 4–9% body-weight reduction, modest HbA1c improvement, modestly lower insulin requirements, and more time-in-range on CGM — at the cost of more hypoglycemia unless insulin is proactively dose-reduced. There is no ADA endorsement, no FDA label, and PA approval is almost universally denied. This article walks through what the evidence shows, what the practical hypoglycemia and DKA considerations are, and what a realistic patient-and-endocrinologist plan looks like.

The honest summary

• FDA status: No GLP-1 receptor agonist has an FDA-approved indication for type 1 diabetes. All use is off-label. The ADA 2026 Standards of Care for obesity^[10] discuss obesity pharmacotherapy in adults with diabetes broadly but do not endorse GLP-1s for T1D as an adjunct to insulin.
• Why patients ask: Roughly 20–30% of adults with T1D meet the BMI cutoff for overweight or obesity — the same prevalence as the general population (Fellinger 2019, Wien Klin Wochenschr^[8]). Insulin therapy itself promotes weight gain, and a subset of T1D patients also have features of insulin resistance — sometimes called “double diabetes.”
• Liraglutide in T1D: ADJUNCT ONE^[1] (n=1,398, full insulin) and ADJUNCT TWO^[2] (n=835, capped insulin), both 52-week treat-to-target RCTs, showed liraglutide 1.8 mg produced ~−5 kg vs placebo, modest HbA1c reductions, and lower insulin doses — with more symptomatic hypoglycemia and more hyperglycemia/ketosis events at the highest dose.
• Semaglutide in T1D: Garg 2024^[4] (12-week open-label pilot, n=12) and Al Hayek 2025^[5] (2-year real-world, n=85 with CGM) both show ~5–7% weight reduction, lower insulin requirements, and meaningful gains in time-in-range. The Würtz Yazdanfard 2026 Danish nationwide cohort^[6] of 1,517 T1D adults followed 2018–2024 is the largest dataset published — consistent effectiveness, no DKA signal above baseline T1D rates.
• Tirzepatide in T1D: Acucella 2026 systematic review^[7] aggregated the limited published RCT and real-world evidence. Effect sizes look larger than semaglutide (consistent with the dual GIP/GLP-1 mechanism in T2D and obesity) but the n is small and a dedicated pivotal trial is not complete.
• Hypoglycemia is the main risk. The ADJUNCT trials saw more symptomatic and severe hypoglycemia on liraglutide than placebo. The fix is proactive insulin dose-reduction — typically 10–20% basal and bolus at the start of GLP-1 therapy, retitrated against CGM data weekly.
• DKA is rare but real. Liraglutide's ADJUNCT trials saw a small ketoacidosis signal at the highest dose. Semaglutide cohorts have not shown a DKA excess. The DKA-risk story for T1D adjuncts is dominated by SGLT2 inhibitors (Lei 2025 meta-analysis^[9]), which have an established excess; GLP-1s are not in that category but still require diligent ketone monitoring.
• CGM is mandatory. Every T1D adult on a GLP-1 needs a continuous glucose monitor — both to catch hypoglycemia from insulin-dose-stacking and to demonstrate the time-in-range improvement that justifies continuing therapy.
• Insurance: PA approval for GLP-1 in T1D is denied at >90% of first submission across major commercial and Medicaid plans. Wegovy can sometimes be approved on the FDA obesity indication if BMI criteria are met, independent of the T1D diagnosis — the obesity claim, not a T1D claim.

Why this question exists at all

Type 1 diabetes is an autoimmune disease of pancreatic beta cells, treated with exogenous insulin. Historically the clinical model was thin patients on insulin. That model has shifted. Across modern population data the prevalence of overweight and obesity in adults with T1D matches the general population — Fellinger 2019 (Vienna cohort, Wien Klin Wochenschr^[8]) reported BMI distributions in T1D adults essentially equal to the Austrian general population. Multiple modern T1D Exchange and registry analyses confirm roughly 20–30% of T1D adults meet the BMI cutoff for obesity (BMI ≥ 30) and another 30% are in the overweight range.

Two forces drive this convergence. First, intensive insulin therapy — the standard of care since the DCCT — promotes some weight gain on average. Second, a subset of T1D adults develop features of insulin resistance on top of their autoimmune beta-cell loss. This phenotype is sometimes called “double diabetes” in clinical literature. These patients often need progressively higher insulin doses to maintain glycemic targets and gain weight as they intensify therapy. The clinical question is: can a GLP-1 receptor agonist break the loop — reducing weight, improving insulin sensitivity, and lowering insulin requirements — without unacceptable hypoglycemia or DKA risk? That is what the trials below tested.

The liraglutide trials: ADJUNCT ONE and ADJUNCT TWO

These are the only two large randomized trials of a GLP-1 receptor agonist in adults with T1D, both sponsored by Novo Nordisk and reported in Diabetes Care in October 2016. Their purpose was to support a potential FDA indication for liraglutide as an adjunct to insulin in T1D. That indication was not pursued to approval — the safety profile, especially at the 1.8 mg dose, did not clear the bar for adjunct labeling in T1D.

ADJUNCT ONE (Mathieu 2016^[1]) randomized 1,398 adults with T1D and HbA1c 7.0–10.0% to liraglutide 1.8 mg, 1.2 mg, 0.6 mg, or placebo on top of full insulin therapy for 52 weeks. At week 52, the 1.8 mg dose produced roughly −5 kg vs placebo, HbA1c reductions of about 0.20% (1.8 mg) vs placebo, and lower total daily insulin doses. Symptomatic hypoglycemia was more frequent on liraglutide. Hyperglycemia with ketosis was also numerically more frequent at the 1.8 mg dose — the signal that complicated the regulatory path.

ADJUNCT TWO (Ahrén 2016^[2]) randomized 835 adults to liraglutide 1.8, 1.2, or 0.6 mg vs placebo for 26 weeks, this time with capped insulin (investigators were instructed not to up-titrate insulin to compensate). HbA1c reductions vs placebo were larger in this design (about −0.35% at 1.8 mg), weight reductions about −5 kg vs placebo, and insulin-dose differences widened. Hypoglycemia rates were again higher on liraglutide.

Dejgaard 2021^[3] pooled the two trials and examined which baseline characteristics predicted response. The largest weight and HbA1c benefits were in patients with higher BMI, longer T1D duration, and higher insulin requirements — the “double diabetes” phenotype. The hypoglycemia signal was consistent across subgroups and is dose-dependent.

The semaglutide evidence

Semaglutide has no dedicated phase 3 T1D program. The evidence comes from a pilot RCT, a 2-year real-world CGM study, and a nationwide cohort.

Garg 2024^[4] (Diabetes Technol Ther) was a 12-week open-label pilot in 12 adults with T1D and BMI ≥ 27, using semaglutide titrated to 1.0 mg weekly. Body weight, HbA1c, and total daily insulin all declined; CGM-measured time-in-range improved. The trial was small but mechanistically clean.

Al Hayek 2025^[5] (J Diabetes Complications) reported 2-year real-world outcomes in 85 adults with T1D started on semaglutide as add-on therapy. Key findings: HbA1c reduction sustained at 24 months, time-in- range improvement of approximately 10 percentage points, weight reductions averaging 6–8%, and lower total daily insulin doses. No excess severe hypoglycemia after the initial dose-adjustment period. No DKA signal.

Würtz Yazdanfard 2026^[6] (Lancet Reg Health Eur) is the largest dataset. The team used Danish national registries to follow 1,517 adults with T1D initiating semaglutide between 2018 and 2024. Findings: sustained reductions in weight, HbA1c, and insulin requirements; no excess in severe hypoglycemia or hospitalized DKA compared with matched controls. This is the most reassuring safety dataset to date.

Tirzepatide in T1D: emerging

Acucella 2026^[7] (Endocrinol Diabetes Metab) systematically reviewed the published tirzepatide T1D data. At the time of review, peer-reviewed evidence consisted of a handful of small open-label studies and retrospective real-world cohorts. The signal is consistent with the semaglutide T1D data and with tirzepatide's effect size in T2D and obesity: larger weight reduction (in the 10–15% range over 6–12 months), HbA1c reduction, and lower insulin needs. The dedicated RCT (Al Ozairi single-centre protocol, BMJ Open 2026^[7]) is active. Until a pivotal trial reads out, tirzepatide use in T1D should be reserved for highly motivated patients under endocrinology supervision with CGM.

Magnitude in context

The hypoglycemia rule: dose-reduce insulin proactively

The single most important practical point in this article: starting a GLP-1 receptor agonist in a T1D patient on insulin without reducing insulin causes hypoglycemia. The ADJUNCT trials documented this clearly — symptomatic hypoglycemia rates were meaningfully higher on liraglutide even on stable insulin doses. The mechanism is that GLP-1 agents improve insulin sensitivity, slow gastric emptying so carbohydrates arrive at the bloodstream later, and suppress appetite so total carbohydrate intake drops.

The standard clinical maneuver, per the way these medications are used in T1D-experienced endocrinology practices, is:

• Basal: reduce by 10–20% on day 1 of GLP-1 therapy. Retitrate against overnight and fasting CGM glucose weekly.
• Bolus / mealtime insulin: reduce insulin-to-carb ratio aggressiveness by 10–20% on day 1. Patients on automated insulin delivery (AID) pumps should adjust the carb ratio in their pump rather than relying on the system to catch up.
• Correction factor: may also need a modest reduction (5–10%) once weight drops 5–7%.
• CGM is mandatory. The dose-adjustment process is data-driven, not symptomatic. Without CGM, the clinician is flying blind and hypoglycemia rates climb.

DKA risk: rare, but ketone monitoring matters

Diabetic ketoacidosis is the catastrophic risk T1D patients and their families fear most. The most-discussed T1D-adjunct DKA risk is from SGLT2 inhibitors (Lei 2025 sotagliflozin meta-analysis^[9]), which carry an established 2–5x excess risk of DKA in T1D and resulted in the EMA withdrawing the T1D indication in 2022. GLP-1 receptor agonists are not in that category. The ADJUNCT liraglutide trials saw a small numerical increase in hyperglycemia-with-ketosis at the 1.8 mg dose, but no meaningful DKA signal at lower doses. The semaglutide cohort data (Al Hayek^[5], Würtz Yazdanfard^[6]) show no excess.

Practical rules:

• Never reduce basal insulin to zero, no matter how good the CGM trace looks. T1D patients always need basal insulin.
• Keep urine or blood ketone strips at home. Check ketones when any glucose reading is > 250 mg/dL with symptoms, or any time the patient feels nauseated or unwell (especially during the GLP-1 titration window when GI side effects are common).
• The dangerous combination is GLP-1 + SGLT2 + insulin omission. SGLT2 inhibitors in T1D are not standard of care for this reason. Adding a GLP-1 to a T1D patient already on an SGLT2 inhibitor requires endocrinology supervision and reinforced ketone-monitoring counseling.

Time-in-range and pump compatibility

Time-in-range (TIR; the percentage of CGM readings in 70–180 mg/dL) is the modern primary outcome for T1D glycemic management. The Al Hayek 2025^[5] 2-year cohort showed TIR improvements of approximately 10 percentage points on semaglutide. The mechanism is twofold: slowed gastric emptying flattens postprandial spikes, and lower carbohydrate intake from appetite suppression reduces total glycemic load.

On pump compatibility: GLP-1 agonists do not interfere with basal-rate logic or with automated insulin delivery (AID) algorithms. Patients using Tandem Control-IQ, Omnipod 5, Medtronic 780G, or Beta Bionics iLet pumps continue using the pump normally. The carb ratio in the pump should be adjusted (typically less aggressive) once weight drops and appetite changes stabilize. Bolus pre-meal insulin should be timed slightly earlier than usual to compensate for the slowed gastric emptying, or split into two doses for very large meals — standard GLP-1 mealtime guidance applies the same way it does in T2D.

A realistic patient action plan

1. Endocrinology, not primary care. Off-label GLP-1 in T1D is not a primary-care prescription. The patient should be working with a board-certified endocrinologist who manages T1D regularly and is familiar with the ADJUNCT and semaglutide-cohort data.
2. CGM mandatory. If the patient is not already on a Dexcom G7, Libre 3+, or equivalent, that should be in place before the GLP-1 is started.
3. Baseline labs and counseling. Pre-start HbA1c, kidney function, lipid panel, and a frank conversation about the ADJUNCT hypoglycemia data and ketone-monitoring rules.
4. Start low, titrate slow. Semaglutide 0.25 mg weekly for 4 weeks, escalating per the standard obesity-program schedule but with insulin dose-reductions ahead of each step.
5. Weekly CGM review. During the first 12 weeks, the endocrinologist or diabetes educator should review CGM data weekly to retitrate insulin.
6. Document the obesity indication. If the patient qualifies on BMI alone (BMI ≥ 30, or ≥ 27 with a weight-related comorbidity), the insurance claim should be filed under the FDA obesity indication for Wegovy or Zepbound, not as a T1D diabetes claim. T1D patients qualify for Wegovy and Zepbound under the obesity indication if they meet BMI criteria; the T1D diagnosis does not exclude them.

Insurance and prior authorization

Prior authorization for a GLP-1 receptor agonist with a primary T1D claim is denied at >90% of first submission across major commercial plans, Medicare Part D, and Medicaid. The reasons are consistent: the medication is not FDA-approved for T1D; the formulary criteria require a T2D or obesity diagnosis; and the plan does not consider ADJUNCT or cohort data sufficient.

The two real-world paths to approval:

• The obesity path. A T1D patient with BMI ≥ 30 (or ≥ 27 with hypertension, dyslipidemia, or sleep apnea) qualifies for Wegovy under the FDA obesity indication. The PA submission should not mention T1D as the reason for the prescription — the reason is chronic weight management. T1D is a comorbidity, not a contraindication, on the obesity label. This works.
• The appeal path for diabetes plans. For Ozempic or Mounjaro under a diabetes benefit, T1D claimants face the FDA-indication mismatch. Some plans will approve on appeal with documentation of failure of adjunctive insulin-sensitizing strategies, BMI criteria, and an endocrinologist letter. The success rate is low (< 30% per published prior-authorization data) but not zero. See our insurance appeal playbook for the letter-of-medical-necessity template.

Bottom line

• No GLP-1 is FDA-approved for type 1 diabetes. All use is off-label.
• The ADJUNCT liraglutide RCTs^[1][2], the Garg 2024 semaglutide pilot^[4], the Al Hayek 2025 2-year real-world cohort^[5], and the Würtz Yazdanfard 2026 Danish nationwide cohort^[6] consistently show 4–9% weight reduction, modest HbA1c improvement, lower insulin requirements, and better CGM time-in-range.
• Tirzepatide T1D data are emerging (Acucella 2026 systematic review^[7]) and look promising but await a pivotal trial.
• Hypoglycemia is the main risk; the fix is proactive insulin dose-reduction of 10–20% on day 1, with weekly CGM-guided retitration.
• DKA risk on GLP-1 in T1D is low; the established DKA-excess story is about SGLT2 inhibitors^[9], not GLP-1s.
• CGM is mandatory; endocrinology supervision is mandatory.
• PA approval is most realistic via the FDA obesity indication if BMI criteria are met. T1D is not a contraindication on the Wegovy or Zepbound label.

Related research and tools

• GLP-1 insurance appeal playbook — letter-of-medical-necessity templates including the T1D off-label use case
• GLP-1 coverage across Medicare, Medicaid, and commercial plans — the formulary landscape and the T2D vs obesity vs T1D indication split
• GLP-1 and diabetic retinopathy — the SUSTAIN-6 retinopathy signal applies to T2D but the FDA-label warning is class-wide and is relevant for T1D patients with pre-existing retinopathy
• What to eat on a GLP-1 — the protein-first eating pattern that applies to T1D patients on GLP-1s the same way it does to obesity- indication patients
• GLP-1 protein calculator — 1.6–2.0 g/kg/day target for lean-mass preservation
• Semaglutide drug page — the FDA label, dose ladder, and approved indications (T2D, obesity, CV-risk reduction; T1D is not on the label)
• Tirzepatide drug page — the FDA label, dose ladder, and approved indications (T2D, obesity, OSA; T1D is not on the label)

Important disclaimer. This article is educational and does not constitute medical advice. Type 1 diabetes is a life-threatening condition. Decisions about adding a GLP-1 receptor agonist or any other medication to an established insulin regimen must be made with a board-certified endocrinologist who manages T1D regularly. Continuous glucose monitoring is required, not optional, for anyone considering this off-label use. Patients should never stop or substantially reduce basal insulin without a clinician's direction; T1D patients always require basal insulin to prevent diabetic ketoacidosis. PMIDs were independently verified against the PubMed E-utilities API on 2026-05-28. The ADA 2026 Standards of Care^[10] do not endorse GLP-1 receptor agonists as adjuncts to insulin in adult T1D, and the FDA labels for Ozempic, Wegovy, Mounjaro, Zepbound, Rybelsus, and Foundayo do not include T1D as an indication.

Last verified: 2026-05-28. Next review: every 12 months, or sooner if a dedicated tirzepatide or semaglutide T1D pivotal trial is published.