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.

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.

What Is "GLP-3"?

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

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 reported substantial weight loss in trials. The selected figures below are not head-to-head comparisons or guaranteed individual outcomes:

• 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: The retatrutide Phase 2 liver substudy included 98 participants with baseline liver fat of at least 10%. At 12 mg, relative liver fat reduction was 82.4% at 24 weeks and 86.0% at 48 weeks. MRI-measured fat reduction does not establish MASH resolution, fibrosis improvement, or superiority over another drug.

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

The proglucagon precursor gives rise to multiple peptides, including glucagon, GLP-1, and GLP-2. The nickname “GLP-3” does not identify another drug target in that sequence.

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 bottom line

Drug Comparison: Single vs Dual vs Triple Agonists

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

The progression explained

These drugs differ in receptor targets, but their separate study results do not isolate the benefit of each additional target:

• Semaglutide (1 receptor): Proved that mimicking GLP-1 could produce significant, sustained weight loss. Approximately 15% body weight reduction.
• Tirzepatide (2 receptors): GLP-1 and GIP activity; 22.5% weight loss at 15 mg in SURMOUNT-1 under the efficacy estimand at 72 weeks.
• Retatrutide (3 receptors): GLP-1, GIP, and glucagon activity; 28.7% at 12 mg in TRIUMPH-4 under the efficacy estimand at 68 weeks in adults with knee osteoarthritis and overweight or obesity without diabetes.

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.

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