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What is GLP-1?

GLP-1 (glucagon-like peptide-1) is a hormone released by the intestine. It helps lower blood sugar after eating and acts in brain areas that control appetite.1 GLP-1 drugs mimic it: semaglutide activates the GLP-1 receptor,2 tirzepatide adds the GIP receptor,3 and retatrutide, still investigational, adds the glucagon receptor as well.45

This page summarizes published sources for information only. It is not medical advice and does not tell anyone to use a product. Questions about your own health belong with a licensed clinician. For questions about an order or a product, contact us.

What GLP-1 does in the body

FDA says medicines that mimic GLP-1 increase insulin release and lower blood sugar after a meal.6 They also slow the passage of food through the gut, which can help a person feel full for longer.6 GLP-1 receptors are also found in brain areas that regulate appetite.6 The insulin and glucagon effects depend on blood sugar: the Ozempic label says semaglutide raises insulin and lowers glucagon in a glucose-dependent way.7

Semaglutide, tirzepatide and retatrutide each have a half-life of about 5 days to 1 week.2315 Semaglutide has two amino acid substitutions compared with human GLP-1.14 The change at position 8 protects it from the DPP-4 enzyme, and a fatty-acid chain makes it bind albumin, a protein in the blood.7 It stays in the circulation for about 5 to 7 weeks after the last maintenance dose.2 Tirzepatide carries a C20 fatty-acid chain that also binds albumin and lengthens its half-life.3 Retatrutide's half-life was about 6 days in a 12-week phase 1b study of 72 adults with type 2 diabetes.15

One, two or three receptors

The three compounds covered in depth here differ in how many hormone receptors they switch on.

Feature Semaglutide Tirzepatide Retatrutide
Receptors activated GLP-12 GIP and GLP-13 GIP, GLP-1 and glucagon4
Half-life About 1 week2 About 5 days3 About 6 days15
Approved brands Ozempic, Rybelsus, Wegovy6 Mounjaro, Zepbound6 None5
Status, October 2026 FDA approved, prescription only2 FDA approved, prescription only16 Phase 3, not approved anywhere5

Semaglutide

FDA approved semaglutide as Ozempic in 2017, as Rybelsus tablets in 2019 and as Wegovy in 2021.6 Ozempic and Rybelsus are labeled for adults with type 2 diabetes.719 The Wegovy injection label covers long-term weight reduction, and lowering the risk of heart attack, stroke and cardiovascular death in adults with heart disease and obesity or overweight.2 It also covers MASH, a fatty liver disease, in adults with moderate to advanced liver scarring but no cirrhosis, under an accelerated approval.2 Read What is Semaglutide?, or the brand pages for Ozempic, Wegovy and Rybelsus.

Tirzepatide

Tirzepatide was approved as Mounjaro in 2022 for type 2 diabetes and as Zepbound in 2023.63 Zepbound is approved for long-term weight reduction in adults with obesity, or with overweight and a weight-related condition.16 It is also approved for moderate to severe obstructive sleep apnea in adults with obesity.16 Read What is Tirzepatide?, or the Mounjaro and Zepbound pages.

Retatrutide

Retatrutide (LY3437943) is an Eli Lilly molecule in phase 3 trials.45 It has not been approved by FDA or any other regulator.5 FDA says it is not a component of any approved drug and has not been found safe and effective for any condition.11 Under federal law, it cannot be used in compounding.11 Lilly plans to submit it for US review in the first quarter of 2027,18 and says neither approval nor that timeline is guaranteed.5 Read What is Retatrutide?.

The wider class

FDA approved the first GLP-1 receptor agonist, Byetta (exenatide), in 2005.6 Its 2024 list adds Victoza (liraglutide, 2010), Trulicity (dulaglutide, 2014) and Saxenda (liraglutide for weight, 2014).6 It also names Adlyxin (lixisenatide, 2016), the insulin combinations Xultophy and Soliqua (2016) and Bydureon BCise (exenatide, 2017).6 Two tablets for weight reduction came later: Wegovy tablets on December 22, 2025, and Foundayo (orforglipron) on April 1, 2026.910 Both are labeled for long-term weight reduction in adults with obesity, or with overweight and a weight-related condition.220

Side effects, benefits and dosage

Nausea, vomiting, diarrhea and other digestive effects are the most common side effects on the labels.716 The labels' boxed warning concerns thyroid C-cell tumors found in rodent studies.7 GLP-1 side effects lists what labels and trials report, with rates against placebo.

Approved uses now reach past blood sugar and weight to heart, kidney, liver and sleep apnea outcomes.2716 GLP-1 benefits and uses sets out those findings use by use, with the evidence behind each, including uses still under study.

Each label starts low and raises the dose in steps, and the prescriber sets the dose for each patient.716 GLP-1 dosage puts the label schedules side by side, along with the doses used in retatrutide trials.

Trial results for weight, including what happened after people stopped treatment, are on GLP-1 and weight loss. The Peptides and weight loss page maps the other compounds people look up with that goal.

Research-labeled and compounded products

FDA says unapproved versions of GLP-1 drugs, including semaglutide and tirzepatide, skip its review of safety, effectiveness and quality.11 It has warned companies that sold semaglutide, tirzepatide, retatrutide, survodutide or mazdutide falsely labeled 'for research purposes' or 'not for human consumption'.11 Those products went to consumers with dosing instructions.11 FDA describes those products as of unknown quality and possibly harmful.11 In February 2026, FDA added that companies cannot claim compounded products are generic versions of, or the same as, approved drugs.17 The label facts on these pages apply only to the approved medicines they come from.11

Comparisons and terms

Side-by-side pages cover the brands and their active ingredients, for example GLP-1 vs Semaglutide, GLP-1 vs Mounjaro, Ozempic vs Wegovy and Mounjaro vs Ozempic. Every comparison is listed on Compare GLP-1 medicines. Terms such as boxed warning, GIP and dose escalation are defined in the peptide glossary.

More on GLP-1

  • GLP-1 side effects

    Side effects of GLP-1 as reported in labels, trials and published studies, with links to the full profile. Reviewed by a qualified reviewer.

  • GLP-1 benefits and uses

    What published sources report about GLP-1 and its uses, with the evidence level of each finding. No promises.

  • GLP-1 dosage

    Published dosing information for GLP-1 from labels and studies, with its source, and why it is not advice for you.

Profiles to read

Comparisons

  • Compare GLP-1 medicines

    Side by side comparisons of Ozempic, Wegovy, Rybelsus, Mounjaro, semaglutide and tirzepatide: what each is, form, maker and approval status.

Frequently asked questions

What does GLP-1 stand for?

GLP-1 stands for glucagon-like peptide-1. It is a natural hormone made in the intestine. After a meal it helps bring blood sugar down, and it signals brain areas that regulate appetite and food intake.1 People also use GLP-1 as shorthand for the medicines that copy the hormone, which FDA calls GLP-1 receptor agonists. Semaglutide and liraglutide are two examples.6

Is semaglutide a GLP-1 inhibitor?

No. Semaglutide is a GLP-1 receptor agonist: it switches the receptor on instead of blocking it. The Wegovy label describes it binding to the GLP-1 receptor, the same receptor the body's own hormone uses, and activating it.2 The Ozempic label adds that semaglutide shares 94% of its amino acid sequence with human GLP-1.7

Is tirzepatide a GLP-1 medication?

Yes, and it also acts on a second receptor. Its label calls tirzepatide a GIP receptor and GLP-1 receptor agonist, so it switches on two hormone receptors instead of one.3 FDA lists Mounjaro and Zepbound among the approved GLP-1 receptor agonists, with a note that tirzepatide is a dual GIP and GLP-1 agonist.6 In lab binding studies it bound the GIP receptor about as strongly as natural GIP.8 It bound the GLP-1 receptor about 5 times more weakly than natural GLP-1.8

Which GLP-1 medicines are FDA approved?

FDA's January 2024 table of approved GLP-1 receptor agonists names exenatide (Byetta, Bydureon BCise), liraglutide (Victoza, Saxenda), dulaglutide (Trulicity) and lixisenatide (Adlyxin).6 It also names two insulin combinations (Xultophy, Soliqua), semaglutide (Ozempic, Rybelsus, Wegovy) and tirzepatide (Mounjaro, Zepbound).6 Wegovy tablets followed on December 22, 2025, and Foundayo (orforglipron) tablets on April 1, 2026.910 Wegovy, Zepbound and both new tablets are prescription only.291016 Retatrutide is not a component of any FDA-approved drug.11

Are GLP-1 drugs banned in sport?

Not as of October 2026. GLP-1 receptor agonists, including semaglutide and tirzepatide, are not on the World Anti-Doping Agency Prohibited List.1213 WADA said in September 2026 that their status stays the same for 2027 while it gathers data on athletes.12 WADA's 2026 list does not name retatrutide.13 Its S0 class, though, bans at all times substances with no current approval from any government health regulator for human treatment, such as drugs in clinical development.13 S0 applies when no other section of the list covers the substance.13 Retatrutide has no such approval.5

Written by D2C Peptides Editorial Team.

Pending qualified review.

Updated .

Sources

  1. FDA Requests Removal of Suicidal Behavior and Ideation Warning from Glucagon-Like Peptide-1 Receptor Agonist (GLP-1 RA) Medications (Drug Safety Communication, 01-13-2026). U.S. Food and Drug Administration, 2026.
  2. WEGOVY (semaglutide) injection and tablets, prescribing information (revised 6/2026). U.S. National Library of Medicine, DailyMed (label by Novo Nordisk), 2026.
  3. MOUNJARO (tirzepatide) injection, prescribing information (revised 8/2026). U.S. National Library of Medicine, DailyMed (label by Eli Lilly), 2026.
  4. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism (PubMed record, National Library of Medicine), 2022.
  5. Is retatrutide available in the consumer market? (Lilly Medical answer, last reviewed August 4, 2026). Eli Lilly and Company (Lilly Medical), 2026.
  6. Update on FDA's ongoing evaluation of reports of suicidal thoughts or actions in patients taking a certain type of medicines approved for type 2 diabetes and obesity (Drug Safety Communication, 01-11-2024). U.S. Food and Drug Administration, 2024.
  7. OZEMPIC (semaglutide) injection, prescribing information (revised 5/2026). U.S. National Library of Medicine, DailyMed (label by Novo Nordisk), 2026.
  8. Coskun et al. 2018, receptor binding results. Molecular Metabolism, 2018.
  9. Drugs@FDA: NDA 218316 (WEGOVY, semaglutide tablets). U.S. Food and Drug Administration, 2025.
  10. Drugs@FDA: NDA 220934 (FOUNDAYO, orforglipron calcium). U.S. Food and Drug Administration, 2026.
  11. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. U.S. Food and Drug Administration, 2026.
  12. WADA publishes 2027 Prohibited List. World Anti-Doping Agency, 2026.
  13. World Anti-Doping Code International Standard: Prohibited List 2026. World Anti-Doping Agency (copy hosted by the Czech National Sports Agency), 2025.
  14. Discovery of the Once-Weekly Glucagon-Like Peptide-1 (GLP-1) Analogue Semaglutide (Lau et al.), PubMed abstract PMID 26308095. Journal of Medicinal Chemistry (abstract via NLM PubMed E-utilities), 2015.
  15. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. The Lancet (PubMed record, National Library of Medicine), 2022.
  16. ZEPBOUND (tirzepatide) injection, prescribing information (revised 8/2026). U.S. National Library of Medicine, DailyMed (label by Eli Lilly), 2026.
  17. FDA Intends to Take Action Against Non-FDA-Approved GLP-1 Drugs (FDA Statement, February 6, 2026). U.S. Food and Drug Administration, 2026.
  18. What are the results of retatrutide from TRIUMPH-3 in adults with severe obesity and established cardiovascular disease? (Lilly Medical answer, last reviewed July 23, 2026). Eli Lilly and Company (Lilly Medical), 2026.
  19. RYBELSUS and OZEMPIC (semaglutide) tablets, prescribing information (revised 1/2026). U.S. National Library of Medicine, DailyMed (label by Novo Nordisk), 2026.
  20. FOUNDAYO (orforglipron) tablets, prescribing information (revised 7/2026). U.S. National Library of Medicine, DailyMed (label by Eli Lilly), 2026.