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GLP‑1, GIP and glucagon explained

GLP-1, GIP and glucagon are hormones the body makes itself. They are the basis for the new weight loss injections. Semaglutide acts on GLP-1, tirzepatide on GLP-1 and GIP, and retatrutide on all three. Here is what the hormones do.

Written by The Peptideguiden editors. Last updated 29 October 2026. 1 min.

Contents
  1. What is GLP-1?
  2. What is GIP?
  3. What is glucagon?
  4. Which medicines act on which hormones?
  5. Questions and answers
  6. Sources
A blood glucose meter on a table

In short

  • GLP-1 and GIP are released from the gut when we eat, and raise insulin when blood sugar rises.
  • GLP-1 also slows the emptying of the stomach and helps us feel full.
  • Glucagon raises energy use by mobilising the body’s energy stores.
  • The body’s own hormones are broken down quickly. The medicines are made to last much longer.

What is GLP-1?

GLP-1 is a hormone released from cells in the gut when we eat. It raises the release of insulin and lowers the release of glucagon, so blood sugar is kept in check after a meal. GLP-1 also slows the emptying of the stomach, so we eat less.[1]

What is GIP?

GIP is also a gut hormone, released a few minutes after we eat. Like GLP-1, it raises insulin release when blood sugar rises. GIP also acts directly on fat tissue.[2]

GLP-1 and GIP are called incretins. Both are broken down quickly by the enzyme DPP-4. This is why the medicines are designed to resist this breakdown and last much longer.[2]

What is glucagon?

Glucagon is a hormone from the pancreas. It raises energy use by making the liver produce sugar, increasing fat burning and mobilising the body’s energy stores.[3] In medicines it is combined with GLP-1 to give greater weight loss.

Which medicines act on which hormones?

  • Semaglutide acts on the GLP-1 receptor. It is approved in the EU for type 2 diabetes and overweight.[4][5][6]
  • Tirzepatide acts on the receptors for GIP and GLP-1. It is approved in the EU.[7][8]
  • Retatrutide acts on the receptors for GIP, GLP-1 and glucagon. It is in the last phase of clinical trials.[9]

Questions and answers

What does GLP-1 mean?

Glucagon-like peptide 1. It is a hormone from the gut that raises insulin after meals and helps us feel full.

Are Ozempic and Wegovy the same?

Both contain semaglutide. They are approved for different purposes: Ozempic for type 2 diabetes and Wegovy for overweight.

Is retatrutide approved?

Retatrutide is in the last phase of clinical trials, with large studies in humans.

Sources

  1. [1]

    Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Cell Metab. 2018.

    PMID 29617641DOIReview

  2. [2]

    Baggio LL, Drucker DJ. Biology of incretins: GLP-1 and GIP. Gastroenterology. 2007.

    PMID 17498508DOIReview

  3. [3]

    Wen J, et al. Next generation dual GLP-1/GIP, GLP-1/glucagon, and triple GLP-1/GIP/glucagon agonists: a literature review. Nutr Metab Cardiovasc Dis. 2025.

    PMID 40685266DOIReview

  4. [4]

    Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med. 2023.

    PMID 37952131DOIRCT · n = 17,604 · Funding or ties: Novo Nordisk.

  5. [5]

    Ozempic (semaglutide): EPAR. Authorised in the EU on 08.02.2018. European Medicines Agency (EMA). 2018.

    European Medicines Agency (EMA)Official source

  6. [6]

    Wegovy (semaglutide): EPAR. Authorised in the EU on 06.01.2022. Prescription only. European Medicines Agency (EMA). 2026.

    European Medicines Agency (EMA)Official source

  7. [7]

    Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022.

    PMID 35658024DOIRCT · n = 2,539 · Funding or ties: Eli Lilly.

  8. [8]

    Mounjaro (tirzepatide): EPAR. Authorised in the EU on 15.09.2022. Prescription only. European Medicines Agency (EMA). 2026.

    European Medicines Agency (EMA)Official source

  9. [9]

    Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. 2026.

    PMID 42814954DOIRCT · n = 2,339 · Funding or ties: Eli Lilly.