FAQs: GLP-1–Based Therapies in Type 1 Diabetes

Updated: 10th September 2025

This FAQ explains how GLP-1 and GIP therapies work, their current licensing status, what the latest evidence shows, and how they can be used safely in type 1 diabetes. It has been strongly informed by the expertise of Professor Viral Shah, featured in The Glucose Never Lies® PodcastGLP-1 in T1D (Episode 17).

Disclaimer: This content is educational only. GLP-1–based therapies are not licensed for type 1 diabetes. Any use should be discussed with your healthcare team.

This summary FAQ can be downloaded. It was published on September 10, 2025.

GLP-1RA-GIP-in-Type-1-Diabetes-FAQ-10-9-25pdf

Basics

What are GLP-1 and GIP?

  • GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic peptide) are incretin hormones released after meals.
  • They: stimulate insulin (if β-cell function remains), suppress glucagon, slow stomach emptying, and reduce appetite.
  • Medicines include:
    – GLP-1RAs: liraglutide, semaglutide, dulaglutide, exenatide.
    – Dual GLP-1/GIP: tirzepatide.
    – Triple agonists (GLP-1/GIP/glucagon) in clinical trials.

Are these medicines licensed for people with type 1 diabetes?

No. None are licensed for T1D.

  • All use is off-label.
  • Paediatric/adolescent use: not licensed for T1D; expert groups like ISPAD stress caution and urge new trials.

How do GLP-1–based therapies work in T1D?

  • In T1D, insulin is injected into fat/skin → less insulin reaches the portal vein → higher glucagon and liver glucose release.
  • GLP-1 therapies help by reducing glucagon, slowing digestion, suppressing appetite, and sometimes lowering insulin requirements.
  • This may help smooth post-meal spikes, reduce insulin doses, and support weight loss.

Evidence

What does the clinical evidence show in T1D?

  • ADJUNCT ONE (liraglutide, 52-week RCT) — modest HbA1c drop, weight loss, ↓ insulin; but ↑ hypoglycaemia and ketosis at high doses. PMID: 27506222
  • ADJUNCT TWO (liraglutide + capped insulin, 26-week RCT) — HbA1c −0.3%, weight −5 kg, ↓ insulin, ↑ hypo (1.2 mg), ↑ ketosis (1.8 mg). PMID: 27493132
  • ADJUST-T1D (semaglutide + AID system, NEJM Evidence 2025, 26-week RCT) — No DKA, HbA1c −0.3%, time in range (TIR) +9%, weight −8.8 kg, insulin −22 U/day, PMID: 40550013
  • Semaglutide crossover (Nature Medicine 2025) — improved glucose, but recurrent euglycaemic ketosis. PMID: 39794615
  • Tirzepatide observational (JDST 2025) — HbA1c −0.6%, TIR +12%, weight −10%, insulin −19 U/day; no DKA. PMID: 38317405

What do expert guidelines say?

  • ADA/EASD Consensus (2021) — off-label use should be specialist-led, start low, titrate monthly, reduce insulin cautiously. PMID: 34590174
  • ADA Standards of Care 2025 — regular CGM reviews, lab checks (renal, LFTs, B12, vit D). PMID: 39651989
  • ISPAD 2024 (youth) — only licensed for obesity/T2D ≥10 yrs, not T1D; if used off-label: lowest dose, slow titration, ketone education. PMID: 39884261
  • DTS GLP-1RA+AID Consensus (2025) — start low, go slow; must remain specialist-led; registry data essential. PMID: 39517127

Insulin Adjustments

How much should I reduce insulin when starting a GLP-1?

Typical starting bands:

  • HbA1c >9% or TIR <40% → reduce ~10%.
  • HbA1c 7.5–9% or TIR 40–60% → reduce ~20%.
  • HbA1c <7.5% or TIR >60% → up to ~30%.
  • High hypo risk (TBR >4%) → ~30% with close CGM monitoring.

What if I’m on multiple daily injections (MDI)?

  • Reduce both basal and bolus proportionally.
  • Relax carb ratios and correction factors slightly.
  • Monitor closely with CGM during titration.

What if I’m on a pump or AID system?

  • See the Automated Insulin Delivery (AID) Systems Guide.
  • In general, reduce basal targets more than bolus.
  • Start with higher glucose targets, then step down.
  • System-specific:
    – Tandem X2: create multiple profiles (−10/−20/−30%).
    – Medtronic 780G: lengthen active insulin time; use a higher target.
    – Omnipod / CamAPS: relax carb ratios initially.
    – iLet: /choose “smaller meal” for usual meals, until the algorithm adapts (7-14 days)

What safety checks do I need?

  • Never stop basal insulin.
  • Use CGM with alerts enabled.
  • Test ketones when unwell, with nausea, or unexplained highs.
  • Educate on sick-day rules.

Lifestyle, Nutrition & Training

Do I need resistance training?

Yes. Resistance training helps preserve lean mass, which may otherwise fall with GLP-1–induced weight loss.

How should I change my diet when starting a GLP-1?

  • Smaller, frequent meals may reduce nausea.
  • Limit heavy, fatty meals early in titration.
  • Spread protein evenly across the day.
  • Consider Exercise Carbohydrate Calculators if training.

How much protein should I eat?

  • Target ~1.5 g/kg/day, split across 3–4 meals.
  • Prioritise lean meats, fish, eggs, beans, lentils, dairy, soy.
  • Combine with resistance training for lean mass.
  • See Overcoming Insulin Resistance in T1D.

How do I avoid nutritional deficiencies if appetite is low?

  • Focus on nutrient-dense foods: lean protein, colourful veg, whole grains, nuts, seeds.
  • Use lower-fibre veg if fullness is an issue.
  • Consider a multivitamin.
  • Check labs (renal, LFTs, vit D, iron, B12).

How can I protect my bones?

  • Ensure adequate protein, vit D, calcium.
  • Do resistance training.
  • Consider bone monitoring for long-term therapy, especially in youth.

Side Effects

What are the common side effects?

  • GI: nausea, vomiting, diarrhoea.
  • Appetite suppression → possible undernutrition.
  • Loss of lean mass if diet/training not optimised.
  • Rare: peroneal palsy with rapid weight loss.

How can I manage nausea?

  • Start with lowest dose; titrate slowly (monthly).
  • Eat small, frequent meals.
  • Avoid heavy, fatty meals at initiation.
  • Moderate fibre intake early.

Broader Questions

Is there benefit if I’m a normal weight?

Yes. Benefits can include glucagon suppression, smoother glucose, and reduced insulin needs — but risks of GI side effects are greater without weight-loss goals. Use lowest effective dose, prioritise lean mass protection.

Will a GLP-1 replace insulin?

No. Insulin remains essential in T1D. GLP-1s only reduce the amount needed — never remove basal insulin.

How does this fit with insulin resistance in T1D?

GLP-1s can reduce insulin resistance by lowering weight, reducing glucagon, and improving satiety.
See:

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