Investigational · not FDA approved

Editorially reviewed · Last updated July 22, 2026 · How we review

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" (retatrutide) 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"

	GLP-1	GLP-2	"GLP-3" (Retatrutide)
What is it?	A naturally occurring gut hormone	A naturally occurring gut hormone	An informal consumer nickname for retatrutide — NOT a real hormone
Produced in	L-cells in the intestine, released after eating	L-cells in the intestine, released after eating	Not produced in the body — it is a synthetic drug
Primary function	Stimulates insulin, suppresses glucagon, slows gastric emptying, reduces appetite	Promotes intestinal growth, repair, and nutrient absorption	Activates GLP-1 + GIP + glucagon receptors to reduce appetite and increase energy expenditure
Related to weight loss?	Yes — the foundation of modern weight loss drugs	No — used for intestinal conditions	Yes — the most potent weight loss drug in clinical trials
Associated drugs	Semaglutide (Ozempic/Wegovy), liraglutide (Saxenda)	Teduglutide (Gattex)	Retatrutide (investigational, Eli Lilly)
Scientific term?	Yes	Yes	No — the correct term is "triple agonist" or GLP-1/GIP/glucagon receptor agonist

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.

Drug	Brand Names	Manufacturer	Receptors	Max Weight Loss (Trials)
Semaglutide	Ozempic (diabetes), Wegovy (obesity)	Novo Nordisk	GLP-1 only (single agonist)	~15% (STEP 1, 68 weeks)
Liraglutide	Victoza (diabetes), Saxenda (obesity)	Novo Nordisk	GLP-1 only (single agonist)	~8% (SCALE, 56 weeks)

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

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:

GLP-1 receptor — reduces appetite, improves insulin secretion
GIP receptor (glucose-dependent insulinotropic polypeptide) — further enhances insulin release and may affect fat metabolism
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.

	Single Agonist	Dual Agonist	Triple Agonist
Drug	Semaglutide	Tirzepatide	Retatrutide
Brand names	Ozempic, Wegovy	Mounjaro, Zepbound	Not yet named (investigational)
Manufacturer	Novo Nordisk	Eli Lilly	Eli Lilly
Receptors targeted	GLP-1	GLP-1 + GIP	GLP-1 + GIP + Glucagon
How it reduces weight	Primarily reduces appetite and food intake	Reduces appetite; may also affect fat metabolism via GIP	Reduces appetite AND increases energy expenditure via glucagon receptor
Max weight loss (trials)	~15% (STEP 1)	~22.5% (SURMOUNT-1)	~28.7% (TRIUMPH-4)
FDA status	Approved (2017/2021)	Approved (2022/2023)	Phase 3 trials — not approved
Availability	Widely available	Available	Clinical trials only

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

Is GLP-3 a real thing?

No. There is no GLP-3 hormone or GLP-3 receptor in the human body. "GLP-3" is an informal nickname for retatrutide, a drug that targets three receptors (GLP-1, GIP, and glucagon). The correct term is "triple agonist." We use the term "GLP-3" on this site because it is what many people search for, but it is not scientifically accurate.

Is GLP-2 the same as tirzepatide (Mounjaro)?

No. GLP-2 is a real gut hormone involved in intestinal growth and repair. Tirzepatide (Mounjaro/Zepbound) is a dual-agonist drug that targets GLP-1 and GIP receptors — it has nothing to do with the GLP-2 hormone. The confusion arises because some people use "GLP-2" as shorthand for "a drug targeting 2 receptors," but this is incorrect.

What is the difference between GLP-1 and GLP-3?

GLP-1 is a real hormone that your body produces. "GLP-3" is not a hormone — it is consumer slang for retatrutide, a drug that activates three receptors. In terms of the drugs: semaglutide (a GLP-1 agonist) targets one receptor and produces about 15% weight loss. Retatrutide (informally called "GLP-3") targets three receptors and has produced up to 28.7% weight loss in clinical trials. Retatrutide is not yet FDA-approved.

Why do people say GLP-3 if it is not real?

The term caught on because it follows a simple, memorable pattern: GLP-1 drugs target 1 receptor, so a drug targeting 3 receptors becomes "GLP-3." It was popularized by podcasters and social media creators who were simplifying the science for a general audience. While the shorthand is understandable, it creates confusion with GLP-2, which is a real hormone with a completely different medical purpose.

Is retatrutide better than Ozempic or Mounjaro?

In clinical trials, retatrutide has produced more weight loss than both semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound). However, retatrutide is not yet FDA-approved and cannot be prescribed. Semaglutide and tirzepatide are available today with extensive real-world safety data. Whether retatrutide will ultimately be "better" depends on its long-term safety profile, which is still being established in Phase 3 trials.

Can I get GLP-3 (retatrutide) now?

No. Retatrutide is only available through clinical trial enrollment. It has not been approved by the FDA. Any online source claiming to sell retatrutide is selling an unregulated, unverified product. FDA approval is expected in 2027 at the earliest. For more detail, see FDA Approval Timeline.

Does GLP-2 help with weight loss?

No. GLP-2 promotes intestinal growth and nutrient absorption. It is not involved in appetite regulation or weight management. The only approved GLP-2-based drug (teduglutide/Gattex) is used for short bowel syndrome, a rare intestinal condition. If you are looking for weight loss medication, GLP-1 receptor agonists (semaglutide, tirzepatide) are the currently approved options.

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

How we keep this honest

What this is: Educational information, not medical advice. It reports published research — it doesn’t recommend that you use, obtain, or supply anything.
Regulatory status: Retatrutide and similar peptides are investigational — not approved by the FDA or any regulator. Semaglutide and tirzepatide are prescription-only medicines, available only through a licensed prescriber.
Our standard: Every claim traces to a primary source. We label the strength of evidence and flag estimates as estimates — never as clinical fact.
No commercial ties: We don’t sell, supply, or link to suppliers of any medicine, and aren’t affiliated with any manufacturer.

Do not make decisions about your health without consulting a qualified healthcare provider. For trial enrolment, see ClinicalTrials.gov. More on how we review.

Sources

Grounded in primary sources