FAQs for GLP1 & T1D: Understanding Therapies

Updated: 15 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® Podcast — GLP-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.

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) — HbA1c −0.3%, time in range (TIR) +9%, weight −8.8 kg, insulin −22 U/day, no DKA. 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 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 higher target.
– Omnipod / CamAPS: relax carb ratios initially.
– iLet: enter 20–40% fewer carbs at first.

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.

Aim for 2–4 sessions/week.
Mix compound lifts and bodyweight work.
Combine with aerobic exercise, anaerobic exercise, and mixed sports.
See Exercise and Type 1 Diabetes — Practical Guide.

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:

Overcoming Insulin Resistance in T1D