You have probably heard the brand names before you heard what they do. This page goes the other way: the mechanism first, in ordinary words, then the names.
The hormone
After you eat, cells in your gut release a small protein called glucagon-like peptide-1, GLP-1 for short. It does several things at once. It tells the pancreas to release insulin when blood sugar is high. It slows the rate at which your stomach empties. And it acts on the parts of the brain that decide whether you feel hungry or full. Your own GLP-1 is broken down within minutes, so its effect on any one meal is short.
The medicine
Semaglutide is a made version of GLP-1 with two changes: one stops it being broken down quickly, the other lets it stick to a blood protein so it stays in circulation. The result is a molecule that acts like GLP-1 but lasts about a week (Wegovy label section 12.3, half-life about 1 week). That is why it is injected once a week rather than after every meal.
Tirzepatide does the same trick with two hormones. It acts on the GLP-1 receptor and on the receptor for a second gut hormone, GIP (glucose-dependent insulinotropic polypeptide). The Zepbound label describes it as a GIP receptor and GLP-1 receptor agonist (section 12.1), with a half-life of about 5 days (section 12.3). Once weekly again.
"Agonist" is the word the labels use. It means the molecule switches the receptor on, the way the natural hormone would. You will see "GLP-1 receptor agonist" and "GLP-1 RA" used for the whole class. The beginner glossary has the other terms you will meet.
What you notice
Two effects reach you directly. Appetite falls, and food stays in your stomach longer, so you feel full sooner and for longer. Both come from the same receptor activity that produced the trial results. Both also explain the most common side effects, which are gut side effects: nausea, constipation, diarrhea, vomiting (Wegovy label section 6.1; Zepbound label section 6.1). The week-by-week pages cover when those tend to show up and settle.
The blood sugar effect is glucose dependent: the insulin signal only fires when glucose is high, so on its own a GLP-1 rarely drives sugar too low. The labels flag a higher risk of low blood sugar when the medicine is combined with insulin or a sulfonylurea (Wegovy section 5.4; Zepbound section 5.4), which is a question for your prescriber if you take either.
The four names
| Product | Molecule | What the label is for |
|---|---|---|
| Ozempic | semaglutide | Type 2 diabetes in adults, with diet and exercise; cardiovascular and kidney risk reduction in certain adults with type 2 diabetes (section 1) |
| Wegovy | semaglutide | Weight reduction and maintenance in adults and adolescents 12 and older with obesity, and adults with overweight plus a weight-related condition; cardiovascular risk reduction in adults with established cardiovascular disease and obesity or overweight (section 1) |
| Mounjaro | tirzepatide | Type 2 diabetes in adults, with diet and exercise (section 1) |
| Zepbound | tirzepatide | Weight reduction and maintenance in adults with obesity or overweight plus a weight-related condition; moderate to severe obstructive sleep apnea in adults with obesity (section 1) |
Same molecule, different label, different maximum dose, sometimes a different device. The label population page turns the "for" column into the BMI and diagnosis wording the labels actually use.
Compounded versions
You will also see semaglutide and tirzepatide sold as compounded products, made by a pharmacy rather than by Novo Nordisk or Lilly. FDA does not review compounded drugs for safety, effectiveness or quality before they are sold; they are not FDA approved, and they are not interchangeable with the brand products (FDA, Human Drug Compounding). FormBlends, which runs this site, sells compounded semaglutide and compounded tirzepatide. The brand versus compounded page sets out what that difference means for a beginner, in one place.
If you want the deep version
This site stays at the level a first-time reader needs. For the receptor pharmacology, the approval history with dates, per-label dosing tables and the other agents in the class (liraglutide, dulaglutide, the oral tablets, the molecules still in trials), read the network's encyclopedia, GLP-1s Explained, starting with how the class works.
Questions people ask
Is a GLP-1 medicine a hormone?
It is a made copy of a gut hormone, changed so it lasts about a week instead of minutes. Semaglutide copies GLP-1. Tirzepatide copies GLP-1 and a second gut hormone, GIP.
Do Ozempic and Wegovy contain the same drug?
Yes, both are semaglutide. They are approved for different uses at different doses: Ozempic for type 2 diabetes, Wegovy for weight management and for reducing cardiovascular risk in adults with heart disease and excess weight. Mounjaro and Zepbound have the same relationship with tirzepatide.
Sources
- Wegovy (semaglutide) prescribing information, sections 1, 12.1 and 12.3, Novo Nordisk, DailyMed set id ee06186f-2aa3-4990-a760-757579d8f77b Accessed September 4, 2026.
- Zepbound (tirzepatide) prescribing information, sections 1, 12.1 and 12.3, Eli Lilly, DailyMed set id 487cd7e7-434c-4925-99fa-aa80b1cc776b Accessed September 4, 2026.
- Ozempic (semaglutide) prescribing information, section 1, Novo Nordisk, DailyMed set id adec4fd2-6858-4c99-91d4-531f5f2a2d79 Accessed September 4, 2026.
- Mounjaro (tirzepatide) prescribing information, section 1, Eli Lilly, DailyMed set id d2d7da5d-ad07-4228-955f-cf7e355c8cc0 Accessed September 4, 2026.
- FDA: Human Drug Compounding Accessed September 4, 2026.
Canonical URL: https://formblendsglp1.com/start/what-glp1-medicines-are. Written by the FormBlends editorial team. This page is educational and is not medical advice; see the medical disclaimer.