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The basics

What is GLP-1? How the hormone and the medicines work, in plain English

GLP-1 is a hormone your gut makes after every meal. The medicines named after it, like Ozempic, Wegovy and Zepbound, copy that hormone but last for days instead of minutes. Here is what that means, in plain words.

By 7 min read
Illustration of a stomach and a brain connected by a glowing line.
The short version
  • GLP-1 is a hormone your gut releases after you eat. The body's own GLP-1 lasts only 1.5 to 2 minutes in the blood; GLP-1 medicines are sturdier copies, and semaglutide lasts about 1 week.3,4
  • They help the pancreas release insulin when blood sugar is high, lower glucagon, slow the stomach a little and act on appetite areas in the brain.4,5
  • In two large trials of adults with obesity and no diabetes, average weight loss was 14.9% with semaglutide 2.4 mg (68 weeks) and up to 20.9% with tirzepatide 15 mg (72 weeks).11,12

What is GLP-1?

GLP-1 stands for glucagon-like peptide-1. It is a hormone, a chemical messenger that travels in the blood, made by special cells in the lining of your intestine when food arrives.1 Its main jobs are to help control blood sugar after a meal and to tell your body it has eaten enough.1 "GLP-1" is also shorthand for a group of medicines, such as Ozempic, Wegovy and Zepbound, that copy this hormone.

Illustration of a key fitting into a lock.

What does the natural hormone do?

A research review describes GLP-1 as an incretin: a gut hormone that boosts insulin release after you eat. Insulin is the hormone that moves sugar out of the blood and into your cells. GLP-1 also lowers glucagon, a hormone that tells the liver to release stored sugar. It slows the gut and appears to help regulate appetite and how much you eat.1

The catch is that natural GLP-1 does not last. An enzyme called DPP-4 breaks it down very quickly, even before it leaves the gut.1 The US labels for liraglutide put the half-life of the body's own GLP-1 at 1.5 to 2 minutes.3 Half-life means the time it takes for half of a substance to be cleared from the blood.

What is a GLP-1 medication?

The medicines are called GLP-1 receptor agonists. A receptor is a docking spot on a cell; when the right molecule docks, the cell responds. An agonist is a drug that switches on the same receptor the body's own hormone does. So a GLP-1 receptor agonist sends the same "you have eaten" signal as natural GLP-1.4

The difference is that the medicines were changed so they last. Semaglutide is 94% identical to human GLP-1, but it sticks to albumin, a common blood protein, and resists DPP-4. That protects it from being broken down or filtered out by the kidneys.5 The result is a half-life of about 1 week, according to the Wegovy label.4

An everyday analogy: natural GLP-1 is a key that dissolves within minutes of opening a lock. The medicines are tougher copies of the key that keep working for days. The analogy stops working in one way: the medicine keeps the signal on all week, not just after meals. For why this allows weekly dosing, see GLP-1 half-life explained.

What are the GLP-1 drugs? The main ones in the US

Generic nameBrand namesHow takenApproved uses (US label)Half-life (label)
SemaglutideWegovyWeekly injection or daily tabletWeight management; lowering heart risk in adults with heart disease and obesity or overweight; MASH liver disease (injection)About 1 week
SemaglutideOzempicWeekly injectionType 2 diabetes; heart and kidney risk in type 2 diabetesAbout 1 week
Semaglutide (oral)Rybelsus, Ozempic tabletsDaily tabletType 2 diabetes; heart risk in type 2 diabetesAbout 1 week
TirzepatideZepboundWeekly injectionWeight management; moderate to severe sleep apnea with obesityAbout 5–6 days
TirzepatideMounjaroWeekly injectionType 2 diabetes; heart risk in type 2 diabetesAbout 5 days
LiraglutideVictoza, SaxendaDaily injectionType 2 diabetes (Victoza); weight management (Saxenda)13 hours
DulaglutideTrulicityWeekly injectionType 2 diabetes; heart risk in type 2 diabetesAbout 5 days
OrforglipronFoundayoDaily tabletWeight managementAbout 29–49 hours
 Source: section 1 (Indications) and section 12 (Clinical Pharmacology) of each current US label on DailyMed.3–10 "Weight management" means, per the labels, adults with obesity, or overweight plus at least one weight-related condition, alongside a reduced-calorie diet and more physical activity. Wegovy and Saxenda are also approved for some children aged 12 and older.

Tirzepatide is different from the others. It switches on two receptors: the GLP-1 receptor and the receptor for GIP (glucose-dependent insulinotropic polypeptide), a second gut hormone. Its labels call it a GIP receptor and GLP-1 receptor agonist.7 Orforglipron is also different: it is a pill made from a small chemical compound rather than a peptide (a short protein chain), and its label lists it as a GLP-1 receptor agonist.10 For a closer look at the two best-known medicines, see what is semaglutide and what is tirzepatide. For how the brands line up, see Ozempic vs Wegovy vs Mounjaro vs Zepbound.

How does GLP-1 work in the body?

The labels and reviews describe four main effects:

  • More insulin, but only when blood sugar is high. The Ozempic label says semaglutide boosts insulin and lowers glucagon "in a glucose-dependent manner". In plain terms, the effect is strong when blood sugar is high and fades as it comes back to normal.5 The Wegovy label warns that the risk of low blood sugar rises when semaglutide is combined with insulin or a sulfonylurea.4
  • Less glucagon. Less of this hormone means the liver releases less stored sugar.5
  • A slower stomach. Food leaves the stomach a little more slowly, especially early after a meal, so you stay full longer.5 See GLP-1 and gastric emptying.
  • Appetite signals in the brain. More on this below.

A 2019 review lists further effects, including on the heart, inflammation and reward, many still being studied.2 For blood sugar in more depth, see GLP-1 and insulin resistance.

How does GLP-1 work in the brain?

The Wegovy label says GLP-1 is a natural regulator of appetite and calorie intake, and that GLP-1 receptors sit in several brain areas involved in appetite. In animal studies, semaglutide reached and switched on nerve cells in those areas.4 The Zepbound label says the same for tirzepatide, and notes that GIP receptors are also found in those brain areas.7 Many people describe this as quieter "food noise"; see GLP-1 and food noise.

How does GLP-1 work for weight loss? What the trials found

Feeling full sooner, and so eating less, is the main route. Two landmark trials in adults with obesity or overweight and no diabetes, alongside diet and activity advice, show the size of the effect:

−14.9%average weight change with semaglutide 2.4 mg vs −2.4% with placebo, 68 weeks, 1,961 adults (STEP 1)
−20.9%average weight change with tirzepatide 15 mg vs −3.1% with placebo, 72 weeks, 2,539 adults (SURMOUNT-1)

These are trial averages, and individual results vary widely. For the full results, see how much weight people lose on GLP-1 medication.

Beyond weight, in the SELECT trial of 17,604 adults with heart disease and overweight or obesity but no diabetes, heart attack, stroke or heart death occurred in 6.5% on semaglutide 2.4 mg vs 8.0% on placebo over about 40 months (hazard ratio 0.80).13

What are the side effects?

Stomach and gut symptoms are the most common. In the Wegovy label's pooled weight-loss trials, nausea was reported by 44% of adults on the 2.4 mg injection vs 16% on placebo.4 To reduce these effects, the labels start at a low dose and raise it in steps every 4 weeks; the Wegovy label lists 0.25 mg weekly for the first 4 weeks.4 That is the label's instruction, not advice. The labels also carry a boxed warning about thyroid C-cell tumors seen in rodents.4,7 Read more in GLP-1 nausea and stomach side effects and GLP-1 and thyroid cancer, and for dose steps see the Wegovy and Zepbound dose schedule.

Whether a GLP-1 medicine is right for you, which one, and at what dose, is a decision for you and your prescriber. To see who the labels cover, read who qualifies for a GLP-1. New to the vocabulary? Our GLP-1 glossary explains 40 common terms.

Key terms in this article

  • Hormone: a chemical messenger made in one part of the body that travels in the blood to act on another.
  • Incretin: a gut hormone, like GLP-1 or GIP, that boosts insulin release after eating.
  • Receptor: a docking spot on a cell that responds when the right molecule binds to it.
  • Agonist: a drug that switches on the same receptor as the body's own hormone.
  • Half-life: the time it takes for the amount of a drug in the blood to fall by half.
  • Glucagon: a hormone that tells the liver to release stored sugar into the blood.
  • Glucose-dependent: working only when blood sugar is raised, and fading as it returns to normal.
  • Placebo: a dummy treatment with no active drug, used in trials for comparison.

Common questions

What does GLP-1 stand for?

GLP-1 stands for glucagon-like peptide-1, a hormone made by cells in the gut when you eat. According to the US labels for liraglutide, the body's own GLP-1 lasts only 1.5 to 2 minutes in the blood before enzymes break it down.

What is GLP-1 medication?

GLP-1 medicines are receptor agonists: man-made versions of the hormone that switch on the same receptor but resist breakdown. Semaglutide (Ozempic, Wegovy) has a half-life of about 1 week according to its US label, which is why it can be injected once a week.

How does GLP-1 work for weight loss?

GLP-1 medicines act on appetite areas in the brain and slow the stomach, so people feel full sooner and eat less. In the STEP 1 trial of 1,961 adults with obesity or overweight and no diabetes, weight fell 14.9% on semaglutide 2.4 mg vs 2.4% on placebo over 68 weeks.

What are GLP-1 drugs?

In the US, GLP-1 drugs include semaglutide (Ozempic, Wegovy, Rybelsus), tirzepatide (Mounjaro, Zepbound, which also acts on the GIP receptor), liraglutide (Victoza, Saxenda), dulaglutide (Trulicity) and the daily pill orforglipron (Foundayo). Some are approved for type 2 diabetes and others for weight management.

How does GLP-1 work in the brain?

The US labels for Wegovy and Zepbound say GLP-1 receptors are found in brain areas that regulate appetite, and that in animal studies the drugs reached and activated nerve cells in those areas. Exactly how this works in people is still being studied.

Sources

  1. Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409-1439. doi:10.1152/physrev.00034.2006 · PubMed
  2. Müller TD, Finan B, Bloom SR, et al. Glucagon-like peptide 1 (GLP-1). Mol Metab. 2019;30:72-130. doi:10.1016/j.molmet.2019.09.010 · Full text (PMC)
  3. US prescribing information, section 12.1 (Mechanism of Action) and section 1: VICTOZA and SAXENDA (liraglutide), DailyMed, checked November 2026.
  4. US prescribing information for WEGOVY (semaglutide injection and tablets): boxed warning; sections 1, 2.2, 5.4, 6.1, 12.1 and 12.3. DailyMed, checked November 2026.
  5. US prescribing information for OZEMPIC (semaglutide injection): sections 1 and 12.1. DailyMed, checked November 2026.
  6. US prescribing information for RYBELSUS and OZEMPIC tablets (oral semaglutide): sections 1 and 12.3. DailyMed, checked November 2026.
  7. US prescribing information for ZEPBOUND (tirzepatide): boxed warning; sections 1, 12.1 and 12.3. DailyMed, checked November 2026.
  8. US prescribing information for MOUNJARO (tirzepatide): sections 1, 12.1 and 12.3. DailyMed, checked November 2026.
  9. US prescribing information for TRULICITY (dulaglutide): sections 1, 12.1 and 12.3. DailyMed, checked November 2026.
  10. US prescribing information for FOUNDAYO (orforglipron): sections 1, 11, 12.1 and 12.3. DailyMed, checked November 2026.
  11. Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021;384(11):989-1002. doi:10.1056/NEJMoa2032183 · PubMed
  12. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. doi:10.1056/NEJMoa2206038 · PubMed
  13. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med. 2023;389(24):2221-2232. doi:10.1056/NEJMoa2307563 · PubMed
This article summarises published research for general information. It is not medical advice and does not replace advice from your own care team. Never change a medication or dose without talking to your prescriber.

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