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The basics

GLP-1 glossary: 40 terms explained in plain English

Starting a GLP-1 medicine comes with a lot of new words: agonist, titration, half-life, prior authorization. Here are 40 of them, grouped by topic and explained in plain English.

By 9 min read
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The short version
  • GLP-1 is a gut hormone that lasts only 1.5 to 2 minutes in the blood; GLP-1 medicines copy it but last days, about 1 week for semaglutide.2,3
  • This glossary defines 40 terms in six groups: the medicines, how they work, dosing, measurements, side effects, and insurance and pharmacy.
  • Terms with their own article link to it. Numbers come from US labels, trials and regulators, cited at the end.

What does GLP-1 mean?

GLP-1 stands for glucagon-like peptide-1. It is a hormone made by cells in your gut when you eat; it helps the pancreas release insulin and helps control appetite.1 People also use "GLP-1" as shorthand for the medicines that copy it, such as Ozempic, Wegovy and Zepbound. For the full explainer, read what is GLP-1.

Illustration of a stack of index cards.

The medicines

TermWhat it means
1. GLP-1 receptor agonist (GLP-1 RA)The formal name for the medicine class. An agonist is a drug that switches on the same receptor (a docking spot on a cell) that the body's own hormone does.3
2. SemaglutideA GLP-1 receptor agonist sold as Ozempic (type 2 diabetes), Wegovy (weight management and heart risk) and Rybelsus (a daily diabetes tablet). Its label says it is 94% identical to human GLP-1.3 See what is semaglutide.
3. TirzepatideA weekly injection sold as Mounjaro (type 2 diabetes) and Zepbound (weight management and sleep apnea). It switches on both the GLP-1 and GIP receptors.4 See what is tirzepatide.
4. LiraglutideAn older, daily injection sold as Victoza (type 2 diabetes) and Saxenda (weight management). Its label gives a half-life of 13 hours.2
5. DulaglutideA weekly GLP-1 injection sold as Trulicity, approved for type 2 diabetes and lowering heart risk in type 2 diabetes.5
6. OrforglipronA daily GLP-1 pill sold as Foundayo, approved in the US for weight management. Unlike semaglutide, it is not a peptide (a short protein chain); its label describes a small chemical compound.5 See orforglipron results.
7. Generic name vs brand nameThe generic name is the active ingredient (semaglutide); the brand name is what the company sells it as (Wegovy). One ingredient can have several brands with different approved uses. See Ozempic vs Wegovy vs Mounjaro vs Zepbound.
8. Oral semaglutideSemaglutide as a daily tablet: Rybelsus and Ozempic tablets for type 2 diabetes, and Wegovy tablets for weight management.3 See oral semaglutide for weight loss.
 Sources: section 1 (Indications) and 12.1 (Mechanism of Action) of each US label.2–5

How they work

TermWhat it means
9. IncretinA gut hormone released after eating that boosts insulin release. GLP-1 is one.1
10. InsulinThe hormone from the pancreas that moves sugar out of the blood and into cells. GLP-1 medicines help the body release more of it after meals.3
11. GlucagonA hormone that tells the liver to release stored sugar. GLP-1 medicines lower it when blood sugar is high.3
12. Glucose-dependentWorking only when blood sugar is raised. The Ozempic label says semaglutide raises insulin and lowers glucagon in a glucose-dependent way, so the effect fades as sugar returns to normal.3
13. GIPGlucose-dependent insulinotropic polypeptide, a second gut hormone whose name means it boosts insulin when blood sugar is raised. Tirzepatide acts on its receptor as well as GLP-1's.4
14. DPP-4An enzyme that breaks down natural GLP-1 within minutes. Semaglutide is built to resist it, which is part of why it lasts so long.1,3 See GLP-1 vs SGLT2, DPP-4 inhibitors and metformin.
15. Gastric emptyingHow fast food leaves the stomach. GLP-1 medicines slow it, mostly early after a meal, which helps you feel full.3 See GLP-1 and gastric emptying.
16. Food noiseAn everyday phrase, not a medical term, for constant thoughts about food. The labels say GLP-1 receptors sit in brain areas that regulate appetite.3 See GLP-1 and food noise.

Dosing words

TermWhat it means
17. Subcutaneous injectionA shot into the fatty layer just under the skin. The Wegovy label lists the abdomen, thigh or upper arm.3 See GLP-1 injection sites.
18. Dose escalation (titration)Starting low and raising the dose in steps to reduce stomach side effects. The Wegovy label starts at 0.25 mg weekly for 4 weeks; the Zepbound label starts at 2.5 mg weekly for 4 weeks.3,4 See the dose schedule.
19. Maintenance doseThe dose you stay on after escalation. For adult weight reduction, the Wegovy label lists 1.7 mg or 2.4 mg weekly (up to 7.2 mg), and the Zepbound label lists 5, 10 or 15 mg weekly.3,4 See maintenance dose explained.
20. Half-lifeThe time for half of a drug to clear from the blood. About 1 week for semaglutide and 5 to 6 days for tirzepatide (Zepbound), per their labels.3,4 See GLP-1 half-life.
21. Missed doseA dose not taken on its usual day. Each label has its own rules for what to do, so check yours and ask your pharmacist. See missed a GLP-1 dose.
22. MicrodosingTaking smaller doses than the label lists, a trend seen online. The US labels do not include these doses.3,4 See GLP-1 microdosing.
23. Off-labelUse of a medicine for a purpose, dose or group of people not listed on its approved label, for example Ozempic, a diabetes medicine, prescribed for weight loss alone.
 Doses above are what the US labels list (section 2), not advice. Your prescriber sets your dose.

Measurements

TermWhat it means
24. BMI (body mass index)Weight in kilograms divided by height in meters squared. Trials such as STEP 1 use it to decide who can enroll.6
25. Obesity and overweightIn the trials behind the Wegovy label, obesity meant a BMI of 30 or more and overweight a BMI of 27 to 29.9.3 See who qualifies for a GLP-1.
26. Weight-related comorbid conditionA health problem linked to excess weight, such as high blood pressure or abnormal cholesterol. The weight labels cover overweight only when at least one is present.3
27. Percent body weight lostWeight lost as a share of starting weight, the main result in obesity trials. In STEP 1 it was 14.9% on semaglutide 2.4 mg vs 2.4% on placebo over 68 weeks.6 See weight loss results.
28. PlaceboA dummy treatment with no active drug. Comparing with placebo shows how much of a result is due to the medicine. In SURMOUNT-1, weight fell 20.9% on tirzepatide 15 mg vs 3.1% on placebo over 72 weeks.7
29. A1C (HbA1c)A blood test that reflects your average blood sugar over the past 3 months. The NIDDK says 6.5% or above indicates diabetes.9
30. Lean massEverything in the body that is not fat: muscle, organs, bone and water. In a SURMOUNT-1 scan study of 160 people, about 25% of the weight lost was lean mass, for both tirzepatide and placebo.8 See protein on a GLP-1.
31. DXA scanA low-dose X-ray scan that splits body weight into fat, lean mass and bone. It is how trials measure what kind of weight was lost.8

Side-effect words

TermWhat it means
32. GI side effectsGastrointestinal, meaning stomach and gut, symptoms such as nausea, diarrhea, vomiting and constipation. In the Wegovy label's weight trials, nausea affected 44% on 2.4 mg vs 16% on placebo.3 See GLP-1 nausea.
33. Boxed warningThe FDA's most prominent label warning, printed in a box at the top. GLP-1 labels carry one about thyroid C-cell tumors seen in rodents; whether this happens in humans is unknown.3,4
34. MTC and MEN 2Medullary thyroid carcinoma, a rare thyroid cancer, and multiple endocrine neoplasia type 2, an inherited condition. The labels say not to use these medicines with a personal or family history of either.3,4 See GLP-1 and thyroid cancer.
35. PancreatitisInflammation of the pancreas. The Wegovy label warns of persistent or severe belly pain, sometimes spreading to the back, and says to stop the drug if it is suspected.3 Get medical help promptly if this happens. See gallbladder and pancreatitis.
36. HypoglycemiaLow blood sugar. The Wegovy label counts below 54 mg/dL as clinically significant and says the risk rises when combined with insulin or a sulfonylurea.3

Insurance and pharmacy words

TermWhat it means
37. Prior authorization (PA)Approval your insurer requires before it will pay for a medicine. Your prescriber usually sends records, such as your BMI or A1C, to show you meet the plan's rules.
38. Step therapyAn insurer rule that you must try a cheaper or older medicine first, and show it did not work or was not tolerated, before it covers the one prescribed.
39. FormularyThe list of medicines a health plan covers, often sorted into price tiers. Whether a GLP-1 is covered can depend on what it is prescribed for. See Zepbound and Wegovy cost.
40. CompoundedA version mixed by a pharmacy rather than made by the drug company. The FDA says compounded drugs are not FDA-approved and the agency does not review them for safety, effectiveness or quality before sale.10 See compounded semaglutide and tirzepatide.
This glossary explains words; it does not tell you what to take or change. Decisions about starting, dosing or stopping a medicine belong with your prescriber and pharmacist.

Key terms in this article

  • Hormone: a chemical messenger that travels in the blood from one organ to act on another.
  • Receptor: a docking spot on a cell that responds when the right molecule binds to it.
  • Label (prescribing information): the official FDA-approved document for a medicine, listing its uses, doses and warnings.
  • Peptide: a short chain of amino acids, the building blocks of proteins.

Common questions

What does GLP-1 mean in simple terms?

GLP-1 (glucagon-like peptide-1) is a hormone the gut makes after you eat that helps control blood sugar and tells the brain you are full. The body's own GLP-1 lasts only 1.5 to 2 minutes in the blood, according to the US liraglutide labels, so the medicines are made to last much longer.

What is the difference between a starting dose and a maintenance dose?

A starting dose is the low dose used for the first weeks so the body can adjust; a maintenance dose is the dose you stay on. For example, the US Wegovy label starts at 0.25 mg weekly for 4 weeks and lists 1.7 mg or 2.4 mg weekly as the usual maintenance doses for adult weight reduction.

What does half-life mean for GLP-1 medicines?

Half-life is the time it takes for half of a drug to clear from the blood. The US labels put it at about 1 week for semaglutide and about 5 to 6 days for tirzepatide (Zepbound), which is why both are injected once a week.

Are compounded GLP-1s FDA-approved?

No. The FDA says compounded drugs are not FDA-approved, which means the agency does not review them for safety, effectiveness or quality before they are sold. Approved products such as Wegovy and Zepbound go through that review.

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. US prescribing information, sections 1 and 12.1: VICTOZA and SAXENDA (liraglutide), DailyMed, checked November 2026.
  3. US prescribing information for WEGOVY (boxed warning; sections 1, 2.1, 2.2, 5.2, 5.4, 6.1, 12.1, 12.3, 14), OZEMPIC (sections 1, 12.1) and RYBELSUS / OZEMPIC tablets (section 1). DailyMed, checked November 2026.
  4. US prescribing information for ZEPBOUND (boxed warning; sections 1, 2.1, 2.2, 12.1, 12.3) and MOUNJARO (sections 1, 12.1). DailyMed, checked November 2026.
  5. US prescribing information for TRULICITY (section 1) and FOUNDAYO (sections 1, 11, 12.1). DailyMed, checked November 2026.
  6. 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
  7. 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
  8. Look M, Dunn JP, Kushner RF, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab. 2025;27(5):2720-2729. doi:10.1111/dom.16275 · Full text (PMC)
  9. National Institute of Diabetes and Digestive and Kidney Diseases. The A1C Test & Diabetes. Accessed November 2026.
  10. US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Accessed November 2026.
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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