What Is GLP-1? The Hormone and the Medications, Explained

GLP-1 — short for glucagon-like peptide-1 — is a hormone released by your gut after eating. GLP-1 medications are synthetic peptides that mimic and amplify its effects. This page explains both: the hormone biology and the medications used to treat diabetes and obesity.

Last updated May 1, 2026.

Advertising disclosure: GLP Insights is reader-supported. When you book a consultation or purchase through our partner links, we may earn a commission at no additional cost to you. This does not influence which providers or medications we discuss. Learn how this site is funded.

Talk to a Provider About GLP-1

Licensed providers · All 50 states · No insurance required

✓ Updated monthly with FDA + clinical research ✓ Affiliate-supported, editorially independent ✓ Plain-English explanations of complex medical topics

GLP-1 hormone and receptor mechanism diagram

The Hormone: What GLP-1 Does in Your Body

GLP-1 is a peptide hormone produced by the L-cells of your small intestine, primarily in the jejunum and ileum. When food enters the gut, these cells release GLP-1 into the bloodstream. The natural hormone has a half-life of just 1–2 minutes — it is rapidly broken down by an enzyme called dipeptidyl peptidase-4 (DPP-4).

Despite its short life, GLP-1 has several powerful effects:

Stimulates insulin release from pancreatic beta cells when blood glucose is high
Suppresses glucagon from pancreatic alpha cells, reducing liver glucose output
Slows gastric emptying, prolonging the feeling of fullness
Acts on hypothalamic satiety centers, reducing hunger and food intake
Modest cardiovascular effects on heart rate and vasculature

Why the Natural Hormone Isn't Enough

Because endogenous GLP-1 is broken down within minutes, its effects are brief. In people with type 2 diabetes, the GLP-1 response to meals is blunted further. Researchers reasoned that if you could create a GLP-1 analog that resists DPP-4 — one that lasts hours or days instead of minutes — the effects would be amplified and clinically useful.

The Medications: GLP-1 Receptor Agonists

GLP-1 medications are receptor agonists: they bind the same receptors as natural GLP-1, with modifications that resist DPP-4 breakdown. The current FDA-approved options:

Exenatide (Byetta, Bydureon) — first GLP-1 RA, approved 2005
Liraglutide (Victoza for T2D, Saxenda for obesity)
Lixisenatide (Adlyxin)
Dulaglutide (Trulicity)
Semaglutide (Ozempic, Wegovy, Rybelsus)
Tirzepatide (Mounjaro, Zepbound) — dual GIP/GLP-1 agonist

How GLP-1 Medications Cause Weight Loss

Three mechanisms drive weight loss on GLP-1 receptor agonists:

Reduced appetite. Receptor binding in the hypothalamus and brainstem signals fullness and reduces food craving.
Slower gastric emptying. You feel full longer after meals, which means smaller portion sizes and less snacking.
Possible effects on reward signaling. Emerging research suggests GLP-1 agonists may reduce the rewarding aspects of high-calorie food, alcohol, and other reinforcing substances.

The aggregate effect is meaningful weight loss: about 15% mean body weight reduction with semaglutide 2.4 mg weekly (STEP-1 trial), and about 22% with tirzepatide 15 mg weekly (SURMOUNT-1).

See If You Qualify for GLP-1

Licensed providers · All 50 states · No insurance required

History: A 40-Year Path to Modern GLP-1

GLP-1 was identified in the early 1980s during research into proglucagon, a precursor protein. Its insulinotropic effect was demonstrated soon after. The first practical GLP-1 medication, exenatide, came from an unlikely source: the saliva of the Gila monster lizard, which contains a peptide called exendin-4 that shares structural similarity with human GLP-1 but resists DPP-4. Exenatide (synthetic exendin-4) was approved by the FDA in 2005.

Subsequent compounds (liraglutide, dulaglutide, semaglutide, and the dual agonist tirzepatide) progressively extended half-life and potency. The 2017 approval of weekly semaglutide and 2021 approval of Wegovy for obesity transformed weight management treatment.

Is GLP-1 the Same as Insulin?

No. Insulin is a separate hormone produced by pancreatic beta cells that directly lowers blood glucose. GLP-1 stimulates insulin release in response to food but is not insulin itself. GLP-1 medications can be used alone or alongside insulin, depending on the clinical situation.

GLP-1 vs DPP-4 Inhibitors

Another diabetes drug class — DPP-4 inhibitors (sitagliptin, linagliptin, saxagliptin) — works by blocking the enzyme that breaks down natural GLP-1. DPP-4 inhibitors raise endogenous GLP-1 levels modestly but produce much smaller effects than GLP-1 receptor agonists, and they don't typically cause weight loss.

Side Effects: What to Expect

Common side effects on GLP-1 medications are gastrointestinal: nausea, vomiting, diarrhea, constipation, abdominal discomfort. They are dose-dependent and usually improve with slow titration and time. Less common but more serious risks include pancreatitis, gallbladder events, and the FDA boxed warning regarding thyroid C-cell tumors observed in rodents. Full detail on side effects.

Frequently Asked Questions

What does GLP-1 stand for? +

GLP-1 stands for glucagon-like peptide-1. It is a hormone released by the L-cells in your small intestine after you eat.

What does GLP-1 do in the body? +

GLP-1 stimulates insulin release, suppresses glucagon, slows stomach emptying, and signals satiety to the brain. The net effect is better blood sugar control and reduced appetite.

How do GLP-1 medications work? +

They are GLP-1 receptor agonists — engineered peptides that bind the same receptors as natural GLP-1 but resist rapid breakdown, so the effect lasts hours to days instead of minutes.

Is GLP-1 the same as insulin? +

No. Insulin is a different hormone that directly lowers blood glucose. GLP-1 amplifies insulin release in response to food, among other actions.

When was the first GLP-1 medication approved? +

Exenatide (Byetta) was the first GLP-1 receptor agonist approved by the FDA, in 2005, for type 2 diabetes. Weight management indications followed years later.

Sources

Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metabolism, 2018.
Müller TD et al. Glucagon-like peptide 1 (GLP-1). Molecular Metabolism, 2019.
FDA prescribing information for approved GLP-1 receptor agonists.