Reta peptide: what retatrutide is

What is reta peptide?

"Reta peptide" is the shorthand people use for retatrutide, a synthetic peptide that Eli Lilly is developing under the code LY3437943. It is a single molecule designed to act at three receptors at once: the receptors for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and glucagon. That three-receptor profile is why it is called a triple agonist, and why vendors give it nicknames like GLP-3 RT, which is Astral's name for retatrutide, or GLP-3 (RETA).

Retatrutide is investigational. It has been through phase 3 trials, Lilly has said it plans to file with the FDA in early 2027, and as of November 12, 2026 it is not approved for any use. The rest of this page covers what the molecule is, who developed it, how it is thought to work, what trials have studied, and where laboratories buy it. It contains no dosing, no outcomes and no medical advice.

See GLP-3 RT at Astral →

Retatrutide names and aliases

• Retatrutide: the international nonproprietary name.
• LY3437943: Lilly's development code, used on ClinicalTrials.gov and in the scientific literature.
• Reta: the common nickname.
• Triple agonist or triple G: descriptive names for its GIP, GLP-1 and glucagon receptor activity; PubChem titles its record "Triple G".
• GLP-3 RT, GLP-3 (RETA), GLP-3 (RT), TP-RT3, AP-RTA-3: vendor product names. "GLP-3" is a marketing label, not a hormone; there is no natural GLP-3.

Whatever a label says, the identifiers that pin down the molecule are the CAS number 2381089-83-2 and the molecular formula below. A vendor listing that shows at least one of them, as Astral's does, is telling you what is in the vial.

Who developed retatrutide?

Eli Lilly and Company, the Indianapolis pharmaceutical company, developed retatrutide and sponsors all but one of the 34 LY3437943 studies listed on ClinicalTrials.gov. Lilly's program runs under the TRIUMPH name for obesity-related trials and TRANSCEND for type 2 diabetes trials. In its July 23, 2026 release, Lilly described retatrutide as a once-weekly triple hormone receptor agonist and said it plans to submit a Biologics License Application to the FDA in the first quarter of 2027.

Research vendors selling it are selling a synthesized copy of the published molecule as a laboratory reagent; they have no connection to Lilly and no access to Lilly's clinical material.

How does retatrutide work?

Retatrutide is a peptide agonist, meaning it binds to receptors on cell surfaces and switches them on. Its distinguishing feature is that one molecule activates three different receptors from the same hormone family: the GIP receptor, the GLP-1 receptor and the glucagon receptor. Each of those receptors is normally activated by its own natural hormone. GIP and GLP-1 are gut hormones released after eating; glucagon is the pancreatic hormone that works opposite insulin.

Lilly engineered the molecule to be long-acting. How activating all three receptors together plays out in people is what the clinical program exists to measure, and this page does not report those results. Astral's guide on GLP-1, GLP-2 and GLP-3 explained is a readable primer on the receptor families.

What is retatrutide being investigated for?

As of November 12, 2026, ClinicalTrials.gov lists 34 studies of LY3437943, all but one sponsored by Lilly, ranging from phase 1 pharmacology studies in healthy volunteers to completed and ongoing phase 3 trials. Taken together, the listed conditions include:

• Obesity and overweight, including weight maintenance
• Type 2 diabetes
• Obesity with established cardiovascular disease, and cardiovascular and kidney outcomes
• Knee osteoarthritis
• Obstructive sleep apnea
• Chronic kidney disease
• Metabolic dysfunction-associated steatotic liver disease
• Chronic low back pain in people with obesity or overweight

Representative records are NCT05929079, a completed phase 3 trial in adults with type 2 diabetes and obesity or overweight, and NCT07629401, Lilly's pre-approval expanded access program. Lilly has said its planned FDA submission covers obesity, knee osteoarthritis pain and obstructive sleep apnea. Being investigated for a condition is not the same as being shown to work for it, and nothing here should be read as a claim about results.

What is retatrutide's molecular identity?

Retatrutide is a large modified peptide. PubChem compound 171390338 gives the molecular formula C221H342N46O68 and a molecular weight of about 4,731. The CAS registry number used by chemical suppliers is 2381089-83-2. For a research buyer, these identifiers matter more than any nickname: a listing that gives the CAS number or formula, or at least the LY3437943 code, can be checked against the public record. A listing that gives only "reta" cannot.

Is reta peptide like semaglutide?

They belong to the same family and differ in a specific way. Semaglutide, per its FDA prescribing information, is a GLP-1 receptor agonist: it activates one receptor. Retatrutide activates that receptor and two more, GIP and glucagon. Both are long-acting peptides. The practical differences for a researcher are that semaglutide is an approved, labeled medicine with a public safety record, while retatrutide is investigational, and that their receptor profiles are different enough that findings for one do not transfer to the other.

Reta vs tirzepatide

Tirzepatide is the closer relative. Per its FDA prescribing information, tirzepatide is a dual agonist of the GIP and GLP-1 receptors. Retatrutide adds the glucagon receptor to those two, which is the whole mechanistic difference: dual versus triple. Lilly developed both molecules and is running a phase 3 trial comparing them directly, listed on ClinicalTrials.gov as NCT06662383. Tirzepatide is approved; retatrutide is not. Astral has a longer comparison in its guide to retatrutide vs tirzepatide.

What are the risks of reta peptides?

They are still being measured. Retatrutide's safety profile in people is what Lilly's phase 3 program and its ongoing outcomes trial are characterizing, and the FDA has not reviewed that data. Lilly's own description is that retatrutide is an investigational molecule that cannot be legally sold or marketed for human use. Research-grade material adds a second layer: it is a reagent made to laboratory standards, not a drug made under pharmaceutical manufacturing rules, and no regulator has looked at any vendor's vial. This site does not give medical advice, and no product discussed here is for use in people.

What form is retatrutide supplied in?

Research suppliers sell retatrutide as a lyophilized powder: the peptide is synthesized, purified, dissolved and freeze-dried into a sealed glass vial, labeled by milligrams of peptide. In that form it is stable at room temperature for many months, in Astral's words, and should be refrigerated once reconstituted. Reconstitution uses bacteriostatic water, sold separately; Astral's is Reconstitution Solution (Astral's bacteriostatic water: a 30 mL Hospira vial). For the volume arithmetic, use Astral's peptide calculator rather than guessing.

Where do researchers buy reta peptide?

From research-peptide suppliers that sell it as a reagent for laboratory use. Our where to buy retatrutide page compares six US-facing vendors on sizes and price per mg, and our pick is Astral. Astral synthesizes and manufactures its peptides in the United States, ships from its own New York inventory, and sells GLP-3 RT in 10, 20 and 30 mg vials at $67.99, $117.99 and $157.99. Its listing names the molecule properly and stays inside research-use language, which, after everything above, is the behavior to look for; on those points it is in a class of its own. Before ordering anywhere, read our pages on whether retatrutide is legal to buy and on retatrutide price.

Buy GLP-3 RT at Astral →