What is GLP-3? The retatrutide nickname, explained

"GLP-3" is an informal, scientifically inaccurate nickname for retatrutide, an investigational triple hormone receptor agonist from Lilly that targets the GLP-1, GIP and glucagon receptors. The accurate term is "triple agonist".

If you searched the term after seeing it in a headline or an ad, this page explains where the nickname came from, what the research has actually reported, and what the FDA says about products sold online under that name.

What GLP-3 means: an informal nickname for retatrutide

Lilly addresses the nickname directly. In its own words, "The term 'GLP-3' is a scientifically inaccurate label used informally in the media to describe triple hormone receptor agonists, such as Lilly's retatrutide. This nickname emerged because the medication simultaneously targets three receptors, GLP-1, GIP and glucagon, rather than representing an actual scientific classification."

So the "3" is counting receptor targets. It is not the name of a third hormone in a numbered series.

In the phase 2 obesity trial published in the New England Journal of Medicine in 2023, the molecule appears under its development code, LY3437943, described as an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors.

It is also one molecule, not three drugs combined. The 2023 Lancet phase 2 trial in people with type 2 diabetes describes retatrutide as "a single peptide with agonist activity at the glucose-dependent insulinotropic polypeptide (GIP), GLP-1, and glucagon receptors".

Is GLP-3 a real hormone? What GLP-1, GLP-2 and glucagon are

GLP-1 and GLP-2 are real hormones. Your body makes them by processing a precursor protein called proglucagon.

A 2021 review in Frontiers in Endocrinology puts it this way: "With description of the precursor proglucagon, we now appreciate that glucagon was just the first proglucagon-derived peptide (PGDP) to be characterised. Other bioactive members of the PGDP family include glucagon-like peptides -1 and -2 (GLP-1 and GLP-2), oxyntomodulin (OXM), glicentin and glicentin-related pancreatic peptide (GRPP)".

GLP-3 is not among the peptides that review lists. That is the honest limit of what can be said here: the nickname does not correspond to a hormone named in that family, and Lilly itself says the name comes from the three receptor targets rather than a scientific classification.

One, two or three receptors: how retatrutide differs from tirzepatide and semaglutide

The clearest way to separate these medications is by what they bind to. Tirzepatide is not GLP-3 and it is not a triple agonist. It targets two receptors.

What does the third receptor add? The only description allowed here is an animal one. In a 2022 Cell Metabolism paper, in obese mice, body weight loss with LY3437943 "was augmented by the addition of GCGR-mediated increases in energy expenditure to GIPR- and GLP-1R-driven calorie intake reduction". That is a finding in mice. It has not been described here as a measured effect in people.

If you are weighing the two approved options rather than an investigational one, read tirzepatide vs semaglutide for how those two compare on trial results, side effects and cost.

Is GLP-3 FDA approved? Where retatrutide stands today

No. The FDA's page on unapproved GLP-1 drugs used for weight loss states: "Retatrutide and cagrilintide cannot be used in compounding under federal law. Additionally, these are not components of FDA-approved drugs and have not been found safe and effective for any condition."

Lilly says the same thing from the manufacturer side: "Retatrutide has not been approved by any regulatory agency and is legally available only through Lilly's clinical trials." In practice that means you cannot get it from a pharmacy or a telehealth clinic today.

The FDA has also warned telehealth companies for marketing unapproved drugs such as retatrutide, including instances of direct marketing to consumers. Our explainer on what the FDA statement on unapproved GLP-1 drugs means for you walks through the agency's concerns in plain language.

On the regulatory calendar, there is one dated company statement worth knowing. In a 07-23-2026 release, Lilly said it is completing the manufacturing data package required for a Biologics License Application and "plans to subsequently submit retatrutide in Q1 2027 for U.S. approval". A submission plan is not an approval, and no approval or launch date has been announced.

Products sold online as GLP-3 for research use

Search the nickname and you will find vials for sale. The FDA has warned companies that have illegally sold unapproved drugs containing tirzepatide, semaglutide, retatrutide, survodutide or mazdutide that are falsely labeled "for research purposes" or "not for human consumption". Per the FDA, these products have been sold directly to consumers for human use with dosing instructions.

The point of criticism here is the seller, not the molecule or the science behind it. A research-use label on a consumer purchase does not make the contents a prescription medication, and nobody licensed is accountable for what is in the vial.

Two related reads: GLP-1 supplements vs prescription GLP-1 covers what over-the-counter "boosters" actually are, and how peptide telehealth works shows what a legitimate process looks like, from online visit to a licensed pharmacy shipment.

What retatrutide trials have reported so far

These are results for an investigational drug, reported in published trials. They are not results for any product you can buy, and they are not comparable to results for other medications discussed on this page.

Phase 2 obesity trial, 48 weeks

In the phase 2 obesity trial published in the New England Journal of Medicine in 2023, the least-squares mean percentage change in body weight at 48 weeks was -24.2% in the highest dose group, as compared with -2.1% in the placebo group.

TRIUMPH-1, 80 weeks

TRIUMPH-1 was a phase 3, randomized, double-blind trial in adults with obesity without diabetes, who received a once-weekly subcutaneous injection of retatrutide or placebo for 80 weeks. Results were published online in the New England Journal of Medicine on 09-29-2026.

A total of 2339 participants underwent randomization. The mean percent change in body weight was -25.0% in the highest dose group versus -3.9% in the placebo group.

Side effects reported in those trials

In TRIUMPH-1, the most common adverse events were gastrointestinal. In the phase 2 obesity trial, the most common adverse events in the retatrutide groups were also gastrointestinal, and those events were dose-related and mostly mild to moderate in severity. That trial also reported dose-dependent increases in heart rate that peaked at 24 weeks and declined thereafter.

If you want a weight loss medication now: tirzepatide and semaglutide

Belle does not offer retatrutide. Belle offers compounded tirzepatide and compounded semaglutide, prepared by licensed compounding pharmacies. Compounded medications are not FDA approved finished products. A licensed provider determines eligibility. Compounded medications are not evaluated by the FDA for safety or effectiveness. See Belle's important safety information.

The FDA describes compounding as a practice in which a licensed pharmacist, a licensed physician or, in the case of an outsourcing facility, a person under the supervision of a licensed pharmacist, combines, mixes or alters ingredients of a drug to create a medication tailored to the needs of an individual patient. The agency notes compounded drugs are not FDA approved, which means it does not review their safety, effectiveness or quality before they are marketed.

A clinician decides who qualifies after reviewing your history, labs where appropriate and current medications. Our guide to GLP-1 BMI requirements explains the criteria providers typically work from, and the tirzepatide dosage chart explains how doses are written in mg and units.

What this costs

There is no approved retatrutide product, so there is no retatrutide price. Lilly says that upon completion of clinical trials and the regulatory review process, it plans to ensure retatrutide is priced to reflect the overall value to the healthcare system. Anyone quoting you a price for "GLP-3" today is not selling an approved medication.

Belle's current pricing for compounded tirzepatide and compounded semaglutide is shown live below. Compounded medications are not evaluated by the FDA for safety or effectiveness. See Belle's important safety information.

Short answers to the questions people ask most about the nickname. For decisions about your own care, talk with a licensed provider who can review your health history.

Key points

• "GLP-3" is an informal, scientifically inaccurate nickname for retatrutide, an investigational triple hormone receptor agonist from Lilly. The accurate term is "triple agonist".
• GLP-1 and GLP-2 are natural hormones made from proglucagon. GLP-3 is not among the proglucagon-derived peptides listed in a 2021 Frontiers in Endocrinology review.
• Tirzepatide binds to and activates the GIP and GLP-1 receptors, so it is not a triple agonist. Semaglutide is a GLP-1 receptor agonist. Retatrutide acts at three receptors.
• The FDA says retatrutide cannot be used in compounding under federal law, is not a component of FDA-approved drugs, and has not been found safe and effective for any condition. Lilly says it is legally available only through its clinical trials.
• Belle does not offer retatrutide. Belle offers compounded tirzepatide and compounded semaglutide after a licensed provider reviews your eligibility.

Q: Is reta a GLP-3?

A: No, not in any scientific sense. Lilly calls "GLP-3" a scientifically inaccurate label used informally in the media to describe triple hormone receptor agonists such as retatrutide. The nickname emerged because the medication simultaneously targets three receptors, GLP-1, GIP and glucagon. The accurate term is triple agonist.

Q: Is GLP-3 a real hormone?

A: GLP-1 and GLP-2 are real hormones made from the precursor proglucagon, alongside glucagon, oxyntomodulin, glicentin and GRPP, according to a 2021 Frontiers in Endocrinology review. GLP-3 is not among the proglucagon-derived peptides that review lists. The term is a media nickname for a drug, not a named member of that hormone family.

Q: Is tirzepatide a GLP-3?

A: No. Tirzepatide is not a triple agonist. Its prescribing information states that tirzepatide selectively binds to and activates both the GIP and GLP-1 receptors, which is two receptors, not three.

Q: Is GLP-3 FDA approved?

A: No. The FDA states that retatrutide is not a component of FDA-approved drugs and has not been found safe and effective for any condition. Lilly states that retatrutide has not been approved by any regulatory agency and is legally available only through Lilly's clinical trials. In a 07-23-2026 release, Lilly said it plans to submit retatrutide in Q1 2027 for U.S. approval.

Q: Can GLP-3 be compounded?

A: No. The FDA states that retatrutide and cagrilintide cannot be used in compounding under federal law. The agency has also warned telehealth companies for marketing unapproved drugs such as retatrutide, including instances of direct marketing to consumers.

Q: What are the side effects of GLP-3?

A: Only trial data exists. In TRIUMPH-1, the most common adverse events were gastrointestinal. In the 2023 phase 2 obesity trial, the most common adverse events in the retatrutide groups were gastrointestinal, were dose-related and were mostly mild to moderate in severity, and dose-dependent increases in heart rate peaked at 24 weeks and declined thereafter. These are findings in supervised clinical trials of an investigational drug.

Q: How much does GLP-3 cost?

A: There is no approved retatrutide product and no price. Lilly says that upon completion of clinical trials and the regulatory review process, it plans to ensure retatrutide is priced to reflect the overall value to the healthcare system. Belle does not offer retatrutide. Current Belle pricing for compounded tirzepatide and compounded semaglutide is shown on the price table in this article and on each product page.