GLP-1 basics

What is a GLP-1? How Ozempic, Wegovy, Mounjaro & Zepbound work

Written by Tonic Editorial Updated June 28, 2026

Key takeaways

  • GLP‑1 is a natural gut hormone. It’s made by intestinal cells near the stomach when food is present, helps the body release insulin, and briefly slows how fast the stomach empties.4
  • GLP‑1 medicines copy that hormone. Drugs that mimic its effects are called GLP‑1 receptor agonists; they help the pancreas release insulin, slow stomach emptying, and may decrease appetite.1,4
  • Two common ingredients, several brands. Semaglutide is sold as Ozempic and Wegovy (injection) and Rybelsus (tablet); tirzepatide is sold as Mounjaro and Zepbound.1,2,3
  • Approved uses differ by brand — from type 2 diabetes to weight management, lowering heart risk, and obstructive sleep apnea.1,3

What is a GLP-1?

A GLP‑1 is a hormone your own body makes. According to NIDDK, it’s produced by intestinal cells close to the stomach, and only when food is present.4

It does a few jobs at once. NIDDK describes how GLP‑1 boosts the release of insulin — the hormone that helps move sugar out of your blood — when glucose rises, and notes that it “briefly slows stomach emptying, delaying digestion for a few minutes.”4

When people say “a GLP‑1” as shorthand for a medicine, they usually mean a GLP‑1 receptor agonist — a drug built to copy this hormone. NIDDK explains that natural GLP‑1 only lasts a few minutes in the bloodstream, so scientists made longer-lasting versions that keep signaling the body’s natural insulin response.4

How do GLP-1 medicines work?

They act like the natural GLP‑1 hormone. MedlinePlus places semaglutide and tirzepatide in a class it calls “incretin mimetics” — meaning they mimic the body’s incretin hormones.1,3

MedlinePlus describes three main effects: the medicine helps “the pancreas to release the right amount of insulin when blood sugar levels are high,” it “slows the emptying of the stomach,” and it “may decrease appetite.”1,3

The oral tablet form works in a similar way. MedlinePlus says oral semaglutide helps the pancreas release insulin and works “by slowing the movement of food through the stomach.”2

Ozempic, Wegovy, Rybelsus, Mounjaro, Zepbound — what’s the difference?

The brand names you see in ads are products built around one of two active ingredients. Semaglutide is the ingredient in the injections sold as Ozempic and Wegovy, and in the tablet sold as Rybelsus.1,2

Tirzepatide is the ingredient in Mounjaro and Zepbound.3 Most are given as a liquid in a prefilled pen injected under the skin once a week; Rybelsus is the version taken as a tablet by mouth.1,2,3

The approved uses aren’t identical across brands. MedlinePlus lists semaglutide for controlling blood sugar in certain people with type 2 diabetes, for weight loss in certain people who are obese or overweight, and to reduce the risk of heart attack, stroke, or death in adults with type 2 diabetes and heart and blood vessel disease.1 For tirzepatide, MedlinePlus adds a third approved use: treating obstructive sleep apnea in adults with obesity.3 Which product fits which use is a decision for you and your clinician.

Frequently asked

Is GLP-1 a drug or a hormone?

Both, depending on context. GLP-1 itself is a natural hormone your gut makes when you eat; NIDDK says it is produced by intestinal cells near the stomach and helps release insulin. When people say "a GLP-1" about a medicine, they mean a GLP-1 receptor agonist — a drug designed to copy that hormone's effects.

Are Ozempic and Wegovy the same medicine?

They share the same active ingredient, semaglutide. MedlinePlus lists both Ozempic and Wegovy as brand names for injectable semaglutide, and Rybelsus as the tablet form. They are marketed as separate products with different approved uses, so the right one is a question for your clinician.

How do these medicines affect appetite and digestion?

MedlinePlus says semaglutide and tirzepatide slow the emptying of the stomach and may decrease appetite, in addition to helping the pancreas release the right amount of insulin when blood sugar is high. NIDDK notes the natural GLP-1 hormone also briefly slows stomach emptying.

Sources

  1. Semaglutide Injection — MedlinePlus Drug Information — NIH MedlinePlus
  2. Semaglutide (oral) — MedlinePlus Drug Information — NIH MedlinePlus
  3. Tirzepatide Injection — MedlinePlus Drug Information — NIH MedlinePlus
  4. Story of discovery: medications for diabetes and obesity from research on one pancreatic hormone — NIDDK (NIH)