What Is GLP-1? The Hormone and the Drugs Explained

Key points

• The natural hormone has a half-life of 1.5 to 2 minutes. Semaglutide, the medicine in Ozempic and Wegovy, has a half-life of about one week.
• Tirzepatide, in Mounjaro and Zepbound, switches on the GLP-1 receptor and a second gut hormone receptor called GIP.
• Three kinds of GLP-1 pill are now sold in the US: oral semaglutide for type 2 diabetes (Rybelsus), Wegovy tablets and Foundayo.
• Every GLP-1 drug label we checked, except Byetta, has a boxed warning on thyroid C-cell tumors. The peptide drugs caused these tumors in rats or mice. Foundayo did not, but its label keeps the warning for the drug class.
• In trials, people lost weight on average, and in one study most of that loss came back within a year of stopping.

Sources: Victoza FDA label; Saxenda FDA label; Trulicity FDA label; Ozempic FDA label; Rybelsus and Ozempic tablets FDA label; Wegovy FDA label; Mounjaro FDA label; Zepbound FDA label; Foundayo FDA label; Byetta FDA label; STEP 1 extension, Diabetes, Obesity and Metabolism, 2022

What does GLP-1 stand for?

GLP-1 stands for glucagon-like peptide-1. The name ties it to glucagon, a hormone that raises blood sugar. Both are cut from the same larger protein, called proglucagon, which one gene makes.

It is a peptide, which means a short chain of amino acids. Researchers describe it as 30 or 31 amino acids long, depending on the form. Special cells in the gut lining, called L cells, make it and send it out after a meal.

GLP-1 belongs to a family called incretins. These are gut hormones that tell the pancreas to release insulin after eating. GIP is the other main one.

Sources: Holst, Physiological Reviews, 2007; Mojsov, Weir and Habener, Journal of Clinical Investigation, 1987

What does GLP-1 do in the body?

It has four main jobs, according to research reviews and FDA labels. The Byetta label, for one, says that once the gut releases incretins such as GLP-1 into the blood, they boost insulin in step with blood sugar. The four jobs are:

• Insulin when needed. It boosts insulin release when blood sugar is high. The Victoza label says this effect fades as blood sugar drops back toward normal.
• Less glucagon. It holds back glucagon, the hormone that pushes blood sugar up.
• A slower stomach. It slows gastric emptying, the pace at which food leaves the stomach.
• Fullness. GLP-1 receptors sit in brain areas that control appetite. The Wegovy label calls GLP-1 a natural regulator of appetite and calorie intake.

The natural hormone does not last long. A half-life is the time it takes the body to clear half of a substance. For GLP-1 (7-37), the Victoza label puts it at 1.5 to 2 minutes. Enzymes such as DPP-4 break it apart, and the Holst review says much of it is broken down before it even leaves the gut.

A 2019 review by Mueller and colleagues lists more roles, tied to the kidneys, the heart and the brain. It calls GLP-1 a hormone with many jobs beyond insulin.

Sources: Byetta FDA label; Victoza FDA label; Wegovy FDA label; Holst, Physiological Reviews, 2007; Mueller and colleagues, Molecular Metabolism, 2019

An example: one meal compared with one weekly shot

Picture a lunch of rice and grilled fish. As the food reaches the gut, L cells release GLP-1. That helps insulin rise to handle the sugar from the rice, and the stomach empties more slowly. Within minutes, DPP-4 has broken most of the hormone down. The signal fades until the next meal.

A weekly drug works on a different clock. Semaglutide's half-life is about one week, per the Wegovy label. So the signal does not rise and fall with each meal. It stays on day and night. The label adds that traces stay in the blood 5 to 7 weeks past the final shot.

By our math, a one-week half-life is about 5,000 to 6,700 times longer than 1.5 to 2 minutes. That gap is the core difference between GLP-1 the hormone and GLP-1 the drug.

Sources: Holst, Physiological Reviews, 2007; Victoza FDA label; Wegovy FDA label

How is GLP-1 the hormone different from a GLP-1 drug?

They act on the same receptor, but almost everything else differs. The biggest gaps are how long each one lasts and how it gets into the body.

Sources: Holst, Physiological Reviews, 2007; Victoza FDA label; Byetta FDA label; Wegovy FDA label; Mounjaro FDA label; Foundayo FDA label; Drugs@FDA, Byetta, NDA 021773

What are GLP-1 drugs?

GLP-1 drugs are medicines that bind to the GLP-1 receptor and switch it on. Their labels call them GLP-1 receptor agonists. An agonist is a substance that turns a receptor on, the way the body's own signal would.

Most are copies of GLP-1 with small changes. The Ozempic label says semaglutide shares 94 percent of its sequence with human GLP-1. The Victoza label puts liraglutide at 97 percent. In semaglutide, one change guards against DPP-4, and a fatty chain makes it stick to albumin, a protein in the blood. That slows how fast the kidneys clear it. Dulaglutide skips the fatty chain and leans on sheer bulk instead, fused to part of an antibody, as our Trulicity guide shows.

Exenatide came from nature. Its label says it was first found in a lizard, the Gila monster. In 1992, a team led by John Eng isolated the peptide, called exendin-4, from the lizard's venom. Our exenatide explainer shows how one building block lets that lizard peptide outlast human GLP-1.

Tirzepatide is a dual agonist. Its label says it switches on both the GIP and GLP-1 receptors. For the details, see how tirzepatide works.

Orforglipron, sold as Foundayo, is the odd one out. Its label shows a small chemical molecule, not a chain of amino acids, with a molecular weight of about 902. Semaglutide weighs about 4,114 and tirzepatide about 4,814 on the same scale. Compare it in orforglipron vs tirzepatide.

Retatrutide adds a third target, the glucagon receptor, and is still in trials. A phase 3 trial of it, TRIUMPH-1, was published in the New England Journal of Medicine in 2026. On 7 November 2026, ClinicalTrials.gov listed 14 phase 3 studies of it, and 9 were still running. An openFDA search of Drugs@FDA data the same day found no approved product that contains it. Read more in GLP-3 explained.

Sources: Ozempic FDA label; Wegovy FDA label; Victoza FDA label; Byetta FDA label; Eng and colleagues, Journal of Biological Chemistry, 1992; Mounjaro FDA label; Foundayo FDA label; TRIUMPH-1 trial, New England Journal of Medicine, 2026; ClinicalTrials.gov, phase 3 studies of retatrutide; Drugs@FDA database

How long does each GLP-1 drug last in the body?

This table puts the natural hormone next to every GLP-1 medicine with a current US label that we found. Each half-life comes from that drug's FDA label. Each date is the first approval in Drugs@FDA.

Half-life shapes the schedule. The Byetta label, at about 2.4 hours, schedules it twice a day. The labels for drugs that last about a week schedule them once a week. The newest pill, Foundayo, lasts 29 to 49 hours, which is shorter than the weekly shots.

Left out: products marked discontinued in Drugs@FDA, such as Bydureon BCise and Tanzeum. Also left out are insulin mixes that contain a GLP-1 drug, Soliqua and Xultophy, and lixisenatide on its own, for which we found no current US label.

Sources: Victoza FDA label; Byetta FDA label; Saxenda FDA label; Trulicity FDA label; Ozempic FDA label; Wegovy FDA label; Rybelsus and Ozempic tablets FDA label; Mounjaro FDA label; Zepbound FDA label; Foundayo FDA label; Drugs@FDA, Byetta, NDA 021773; Drugs@FDA, Victoza, NDA 022341; Drugs@FDA, Trulicity, BLA 125469; Drugs@FDA, Ozempic injection, NDA 209637; Drugs@FDA, Rybelsus and Ozempic tablets, NDA 213051; Drugs@FDA, Mounjaro, NDA 215866; Drugs@FDA, Foundayo, NDA 220934; Drugs@FDA, Bydureon BCise, NDA 209210; Drugs@FDA, Tanzeum, BLA 125431

What are GLP-1 drugs approved for?

Each brand has its own list of approved uses, so the same medicine can be approved for different things under two names. In the labels, a major heart event means heart death, a heart attack or a stroke. Every weight approval pairs the drug with a lower calorie diet and more physical activity.

Two points stand out. The Ozempic shot is not approved for weight loss, though Wegovy holds the same medicine; see Wegovy vs Ozempic. And none of these labels lists type 1 diabetes as an approved use. Rules and brands differ outside the US; for Vietnam, see the GLP-1 Vietnam guide.

Sources: Ozempic FDA label; Rybelsus and Ozempic tablets FDA label; Wegovy FDA label; Victoza FDA label; Saxenda FDA label; Trulicity FDA label; Byetta FDA label; Mounjaro FDA label; Zepbound FDA label; Foundayo FDA label

How much weight did people lose on GLP-1 drugs in trials?

Trials report the average share of body weight lost after a fixed time. They do not report how long it takes one person to reach a goal, such as 20 pounds, so no trial can answer that. Three large trials give a sense of scale. Each was paid for by a drug company, and each was published as a full report in the New England Journal of Medicine, a peer-reviewed journal:

• STEP 1, semaglutide (2021). The trial enrolled 1,961 adults with obesity or overweight and no diabetes. After 68 weeks, average weight change was minus 14.9 percent on semaglutide and minus 2.4 percent on placebo. Both groups also had lifestyle support. Novo Nordisk, the maker of semaglutide, funded it.
• SURMOUNT-1, tirzepatide (2022). Adults in this trial started at an average of 104.8 kg. After 72 weeks, average change ran from minus 15.0 to minus 20.9 percent across the three doses tested, against minus 3.1 percent on placebo. Eli Lilly, the maker of tirzepatide, supported it.
• SURMOUNT-5, head to head (2025). In 751 adults with obesity and no diabetes, average change at 72 weeks was minus 20.2 percent on tirzepatide and minus 13.7 percent on semaglutide. Eli Lilly, the maker of tirzepatide, funded this one too.

These are group averages, and people varied a lot. In STEP 1, 86.4 percent of the semaglutide group lost at least 5 percent of their weight, so roughly 1 in 7 did not. In all three trials, the most common side effects were in the gut and were mostly mild to moderate.

For more numbers, see average weight loss on Ozempic and tirzepatide vs semaglutide.

Sources: STEP 1 trial, New England Journal of Medicine, 2021; STEP 1 extension, Diabetes, Obesity and Metabolism, 2022; SURMOUNT-1 trial, New England Journal of Medicine, 2022; SURMOUNT-5 trial, New England Journal of Medicine, 2025

What happens when someone stops a GLP-1 drug?

The STEP 1 extension followed 327 people from both the semaglutide and placebo groups. It tracked them for a year after the drug and the trial's lifestyle program ended. By week 68, those on semaglutide had lost 17.3 percent of their weight on average. The report appeared in Diabetes, Obesity and Metabolism, and its full text says Novo Nordisk funded the STEP 1 trial.

By week 120, the semaglutide group had regained about two-thirds of that loss, for a net loss of 5.6 percent. Most heart and blood sugar markers drifted back toward where they started. The authors said the results fit obesity being a long-term condition.

Sources: STEP 1 extension, Diabetes, Obesity and Metabolism, 2022

What are the side effects and risks of GLP-1 drugs?

The most common side effects are in the gut. The Wegovy label lists those reported by 5 percent or more of people. Nausea, diarrhea, vomiting, constipation and belly pain head the list. It also names headache, tiredness, indigestion, dizziness, bloating, burping, gas, stomach flu, acid reflux, hair loss, odd skin sensations, and low blood sugar in people with type 2 diabetes. The Foundayo pill label lists a similar set.

Labels also warn about rarer, more serious problems:

• Thyroid C-cell tumors. Every label we checked except Byetta's carries a boxed warning on these tumors. For the peptide drugs, such as semaglutide, liraglutide, dulaglutide and tirzepatide, the label says the drug itself caused them in rats or mice. Foundayo is different. Its label says orforglipron has no drug effect in rats or mice and did not cause tumors in rodent studies. Its warning points instead to other drugs of this type, which did cause them in rodents, and notes that orforglipron does act on the human GLP-1 receptor. For every one of these drugs, whether the tumors happen in people is not yet known. The labels say not to use them if the person or a close relative has had medullary thyroid cancer, or if the person has a condition called MEN 2.
• Pancreas and gallbladder. Inflammation of the pancreas has been seen, and gallbladder disease occurred in trials.
• Low blood sugar. The risk goes up when these drugs are used with insulin or with pills that push the pancreas to release insulin.
• Kidneys. Vomiting or diarrhea can cause fluid loss, which can harm the kidneys.
• Surgery. Food or liquid has been breathed into the lungs during general anesthesia or deep sedation.
• Other warnings. Severe gut reactions, allergic reactions, a faster heart rate and eye problems in people with diabetic retinopathy.

One change is recent. The Wegovy label notes that its warning on suicidal behavior and thoughts was removed in February 2026.

Dosing mistakes happen too. America's Poison Centers counted 22,966 GLP-1 exposure cases from 2019 to 2025. It says its most common calls involve accidental errors with FDA-approved drugs, such as doses taken too close together. For a fuller list, see GLP-1 side effects.

Sources: Wegovy FDA label; Foundayo FDA label; Ozempic FDA label; Victoza FDA label; Trulicity FDA label; Mounjaro FDA label; Zepbound FDA label; Byetta FDA label; America's Poison Centers GLP-1 page

Who discovered GLP-1, and when did the drugs arrive?

The path ran from rat studies in the 1980s to lizard venom, then to a weekly shot and finally to pills. In 2024, the Lasker Foundation honored three scientists for the work.

Sources: Mojsov, Weir and Habener, Journal of Clinical Investigation, 1987; Eng and colleagues, Journal of Biological Chemistry, 1992; Drugs@FDA, Byetta, NDA 021773; Drugs@FDA, Victoza, NDA 022341; Drugs@FDA, Ozempic injection, NDA 209637; Drugs@FDA, Rybelsus and Ozempic tablets, NDA 213051; Drugs@FDA, Wegovy injection, NDA 215256; Drugs@FDA, Mounjaro, NDA 215866; Drugs@FDA, Wegovy tablets, NDA 218316; Drugs@FDA, Foundayo, NDA 220934; Lasker Foundation, 2024 award

What about compounded, fake or "research" GLP-1?

A compounded drug is mixed by a pharmacy rather than made by the drug's maker. The FDA says these drugs carry no FDA approval, which means their safety, effectiveness and quality go unreviewed by the agency before they are marketed. For the full story on one example, see compounded tirzepatide.

The FDA has also warned sellers of semaglutide, tirzepatide and retatrutide products whose labels falsely claimed they were "for research purposes" or "not for human consumption". It says these were sold to people for human use and urges consumers not to buy them.

Poison centers report another risk with compounded products. Some people took 10 times the intended amount because the units on a syringe were confusing. To check a pen or vial, see real vs fake GLP-1.

Sources: FDA human drug compounding page; FDA concerns with unapproved GLP-1 drugs; America's Poison Centers GLP-1 page

Can you raise GLP-1 naturally, or with a supplement?

Your body raises GLP-1 every day on its own. Eating is the trigger: L cells release it in response to a meal. Because it breaks down so fast, those natural rises are brief.

Online, some supplements are sold as GLP-1 boosters, and some get nicknames such as the "poor man's Ozempic". A supplement is not a GLP-1 drug, and none appears in Drugs@FDA as one. Under the 1994 US supplement law, the maker, not the FDA, is responsible for a supplement's safety and label before sale. The FDA can act against a product only after it reaches the market.

For what the research says about specific products, see GLP-1 supplements. Many people on these drugs also talk about quieter food noise. That is an everyday term for repeated, unwanted thoughts about food, not a medical diagnosis. A 2025 paper that set out to define it said a formal clinical definition was still lacking.

Sources: Holst, Physiological Reviews, 2007; FDA dietary supplements page; Drugs@FDA database; Dhurandhar and colleagues, Nutrition and Diabetes, 2025

GLP-1 questions

Sources: Ozempic FDA label; Wegovy FDA label; Holst, Physiological Reviews, 2007; Mojsov, Weir and Habener, Journal of Clinical Investigation, 1987; Foundayo FDA label; Rybelsus and Ozempic tablets FDA label; Drugs@FDA, Wegovy tablets, NDA 218316; Drugs@FDA, Foundayo, NDA 220934; SURMOUNT-5 trial, New England Journal of Medicine, 2025