GLP-1 vs GLP-2 vs GLP-3: What's the Difference?

If you have been following the weight loss drug space, you have probably seen the terms GLP-1, GLP-2, and GLP-3 used interchangeably or confusingly. Some of these are real hormones. One of them is not even a real scientific term. This page explains what each one actually means, why the naming is so confusing, and how the drugs associated with each term compare.

The short version: GLP-1 and GLP-2 are real hormones produced in your gut. "GLP-3" is not a hormone at all — it is an informal nickname for retatrutide, a drug that targets three receptors. The "3" refers to the number of receptors the drug activates, not a third type of GLP.

Quick Comparison: GLP-1 vs GLP-2 vs "GLP-3"

What Is GLP-1?

GLP-1 (glucagon-like peptide-1) is a hormone your body naturally produces in L-cells of the small intestine after you eat. It plays a central role in metabolism and blood sugar regulation.

What GLP-1 does in the body:

• Stimulates insulin secretion — signals the pancreas to release insulin in response to food, helping your body process blood sugar
• Suppresses glucagon — reduces the hormone that raises blood sugar, keeping glucose levels stable
• Slows gastric emptying — food stays in your stomach longer, making you feel full for an extended period
• Reduces appetite — acts on appetite-regulating centers in the brain to decrease hunger

GLP-1 receptor agonist drugs

GLP-1 is the hormone that launched the current wave of weight loss medications. Drugs called GLP-1 receptor agonists mimic this hormone, producing the same effects at a much stronger and longer-lasting level than the body produces naturally.

GLP-1 agonism is the foundation that all newer drugs in this class build upon.

What Is GLP-2?

GLP-2 (glucagon-like peptide-2) is the other glucagon-like peptide produced in the gut. It comes from the same precursor molecule (proglucagon) as GLP-1, and it is also released from intestinal L-cells after eating. But it does something completely different.

What GLP-2 does in the body:

• Promotes intestinal growth and repair — stimulates the growth of the intestinal lining (mucosal epithelium)
• Increases nutrient absorption — enhances the gut's ability to absorb nutrients from food
• Reduces intestinal permeability — helps maintain the barrier function of the gut
• Reduces gastric acid secretion — decreases stomach acid production

GLP-2 is NOT related to weight loss

This is a critical distinction. GLP-2 has nothing to do with obesity treatment, appetite suppression, or the weight loss drugs you see in the news. It is an entirely separate therapeutic area.

The only approved GLP-2-based drug is teduglutide (Gattex/Revestive), used to treat short bowel syndrome — a condition where the small intestine is too short (often due to surgical removal) to absorb enough nutrients from food. Teduglutide helps the remaining intestine grow and absorb more, reducing the patient's dependence on intravenous nutrition.

If someone tells you "GLP-2 is the next weight loss drug after GLP-1," they are confusing GLP-2 (a real intestinal hormone) with dual-agonist drugs like tirzepatide. More on this confusion below.

What Is "GLP-3"?

"GLP-3" is not a real biological term. There is no GLP-3 receptor in the human body. There is no GLP-3 hormone. You will not find "GLP-3" in any peer-reviewed medical journal, FDA filing, or pharmaceutical company communication.

"GLP-3" is an informal nickname that emerged in consumer health circles to describe retatrutide, a drug developed by Eli Lilly that activates three hormone receptors simultaneously:

1. GLP-1 receptor — reduces appetite, improves insulin secretion
2. GIP receptor (glucose-dependent insulinotropic polypeptide) — further enhances insulin release and may affect fat metabolism
3. Glucagon receptor — increases energy expenditure, promotes fat breakdown, reduces liver fat

The "3" in "GLP-3" refers to the number of receptors targeted, not a third type of glucagon-like peptide. The correct scientific terminology for retatrutide is a triple agonist or GLP-1/GIP/glucagon receptor agonist.

Why people call it GLP-3

The nickname followed a logical (if inaccurate) pattern:

• Semaglutide targets 1 receptor → people call it a "GLP-1" drug
• Tirzepatide targets 2 receptors → some started calling it "GLP-2" (incorrectly — it has nothing to do with the GLP-2 hormone)
• Retatrutide targets 3 receptors → people started calling it "GLP-3"

The term was popularized through social media, podcasts (notably Andrew Huberman's), and consumer health content. It is catchy and easy to remember, which is why it spread. But it creates real confusion by conflating drug receptor counts with actual hormones — which is why we are writing this page.

Retatrutide's clinical results

Retatrutide has produced the largest weight loss of any anti-obesity medication in clinical trials:

• Phase 2 trial: up to 24.2% body weight loss at 48 weeks (12 mg dose)
• Phase 3 TRIUMPH-4: up to 28.7% body weight loss at 68 weeks (12 mg dose)
• Liver fat reduction: 81-86% in Phase 2 (significantly more than semaglutide or tirzepatide)

As of February 2026, retatrutide is in Phase 3 clinical trials and has not been approved by the FDA. It is not available by prescription. For more detail, see What Is Retatrutide (GLP-3)?.

Why the Naming Is So Confusing

The confusion comes from two separate numbering systems colliding:

System 1: Biological hormones (GLP-1, GLP-2)

In biology, GLP-1 and GLP-2 are two distinct hormones derived from the same precursor molecule, proglucagon. They were named in order of their discovery and characterization. They do completely different things:

• GLP-1 regulates blood sugar and appetite
• GLP-2 promotes intestinal growth and repair

There is no GLP-3 hormone. The proglucagon gene only produces GLP-1 and GLP-2.

System 2: Drug receptor count ("GLP-1", "GLP-2", "GLP-3")

In consumer shorthand, the numbers refer to how many receptors a drug targets:

• "GLP-1 drugs" = single agonists (1 receptor)
• "GLP-2 drugs" = dual agonists (2 receptors)
• "GLP-3 drugs" = triple agonists (3 receptors)

The problem is that these two systems use the same naming convention but mean completely different things. When someone says "GLP-2," they might mean the actual hormone (used for intestinal conditions) or they might mean tirzepatide (a weight loss drug targeting two receptors). These are entirely unrelated.

The bottom line

| Term | Biological meaning | Consumer slang meaning | |---|---|---| | GLP-1 | A gut hormone that regulates appetite and blood sugar | Drugs targeting 1 receptor (semaglutide) | | GLP-2 | A gut hormone that promotes intestinal repair | Drugs targeting 2 receptors (tirzepatide) — incorrect usage | | GLP-3 | Does not exist | Drugs targeting 3 receptors (retatrutide) — not a real term |

Drug Comparison: Single vs Dual vs Triple Agonists

This is what the receptor count actually means in terms of the drugs.

The progression explained

Each generation has added a new receptor target and produced greater weight loss:

• Semaglutide (1 receptor): Proved that mimicking GLP-1 could produce significant, sustained weight loss. Approximately 15% body weight reduction.
• Tirzepatide (2 receptors): Added GIP agonism to GLP-1. Produced approximately 22.5% body weight reduction — roughly 50% more than semaglutide alone.
• Retatrutide (3 receptors): Added glucagon agonism to GLP-1 and GIP. Produced approximately 28.7% body weight reduction. The glucagon receptor is notable because it increases energy expenditure — the body burns more calories at rest — rather than only reducing intake.

This progression is real and meaningful, but the naming pattern ("GLP-1," "GLP-2," "GLP-3") is misleading because it implies these are all related hormones when they are not.

For a more detailed drug-to-drug comparison, see Retatrutide vs Mounjaro vs Ozempic.

Frequently Asked Questions

Sources

• Drucker, D.J. (2006). The biology of incretin hormones. Cell Metabolism. DOI: 10.1016/j.cmet.2006.01.004
• Wilding, J.P.H., et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine. DOI: 10.1056/NEJMoa2032183
• Jastreboff, A.M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine. DOI: 10.1056/NEJMoa2206038
• Jastreboff, A.M., et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. DOI: 10.1056/NEJMoa2301972
• Eli Lilly and Company. (2025). Lilly's retatrutide achieved significant weight loss and pain relief in adults with obesity and knee osteoarthritis. Press release.
• Jeppesen, P.B. (2012). Teduglutide, a novel glucagon-like peptide 2 analog, in the treatment of patients with short bowel syndrome. Therapeutic Advances in Gastroenterology. DOI: 10.1177/1756283X11432700

Medical Disclaimer

The content on glp3.wiki is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Retatrutide is an investigational drug that has not been approved by the U.S. Food and Drug Administration (FDA) or any other regulatory agency.

Do not use this information to make decisions about your health without consulting a qualified healthcare provider. The clinical trial data cited on this page reflects results from controlled research settings and may not reflect real-world outcomes.

If you are considering weight loss medication, talk to your doctor about currently approved options. For information about enrolling in retatrutide clinical trials, visit ClinicalTrials.gov.

This site is not affiliated with Eli Lilly and Company, Novo Nordisk, or any pharmaceutical manufacturer.