What is reta? The peptide behind the nickname, explained

Photograph: editorial illustration for this article. It does not show retatrutide.

Where does the name reta come from?

Reta is simply the first two syllables of retatrutide. The full name follows the convention used for this family of drugs: the suffix -tide marks a peptide, and the stem -tru- is shared with tirzepatide, Lilly's dual agonist sold as Mounjaro and Zepbound. Before it had a name the compound was known by its laboratory code, LY3437943, and that code still appears on every clinical trial record and in the earliest publications^[1].

The nickname spread through forums and social media because retatrutide is long to type and easy to misspell. When people search for reta in a health context, they almost always mean this compound. A second nickname, GLP-3, describes the same molecule and is explained in our article on the GLP-3 peptide.

What is the molecule?

Retatrutide is a single peptide of 39 amino acids built on a GIP backbone, with a C20 fatty diacid attached so that it binds to albumin in the blood and lasts long enough for one injection per week. The discovery paper from Lilly's research group, published in Cell Metabolism in 2022, describes how the sequence was engineered so that one molecule activates three receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor^[1].

That third receptor is the unusual part. Semaglutide acts on one receptor (GLP-1). Tirzepatide acts on two (GIP and GLP-1). Retatrutide adds glucagon, a hormone that raises energy expenditure and pushes the liver to burn fat. The bet, described in the same paper, is that glucagon receptor activity adds weight loss on top of the appetite effect of GLP-1, while the GIP and GLP-1 components keep blood sugar in check despite glucagon's tendency to raise it^[1]. The detail is in our mechanism of action article.

What did reta do in clinical trials?

The result that made reta famous came from the phase 2 obesity trial published in the New England Journal of Medicine in 2023. It enrolled 338 adults with obesity or overweight and no diabetes and followed them for 48 weeks. Mean weight change at 48 weeks was −8.7% on 1 mg, −17.1% on 4 mg, −22.8% on 8 mg and −24.2% on 12 mg, against −2.1% on placebo^[2].

A parallel phase 2 trial in 281 people with type 2 diabetes, published in The Lancet, found HbA1c reductions of about two percentage points on the 8 mg and 12 mg doses at 24 weeks, and a mean weight change of −16.94% on 12 mg at 36 weeks^[3].

Phase 3 then confirmed the direction. On 21 May 2026 Lilly reported topline results from TRIUMPH-1, a trial of 2,339 adults without diabetes registered as NCT05929066: mean weight change at 80 weeks was −19.0% on 4 mg, −25.9% on 9 mg and −28.3% on 12 mg, against −2.2% on placebo. In the 12 mg group, 45.3% of participants lost at least 30% of their body weight^[4][5]. Two further phase 3 trials in people with diabetes and with cardiovascular disease read out in July 2026^[6]. Our trial timeline lists every study with its registry number.

What reta is not

• Not an approved medicine. There is no branded retatrutide product in any pharmacy. Anything labelled reta and sold today is either a clinical trial supply or an unapproved research chemical.
• Not a GLP-1 in the usual sense. The GLP-1 receptor is one of its three targets. Calling it a GLP-1 drug is a simplification that hides the glucagon component, which is the part responsible for several of its side effects.
• Not a supplement. Retatrutide is a synthetic peptide with no food source and no oral form in development that has been published.
• Not a version of Mounjaro. Tirzepatide and retatrutide are different molecules from the same company. See retatrutide vs Mounjaro for the numbers side by side.

What is the legal and regulatory status of reta?

Retatrutide has completed the four TRIUMPH phase 3 trials that were designed to support an obesity application, and a long cardiovascular outcomes trial is still running. In its July 2026 announcement Lilly stated that it plans to submit a Biologics License Application for retatrutide to the FDA in the first quarter of 2027^[6]. Nothing has been filed with the FDA or the EMA at the time of writing, so there is no approved indication, no approved dose and no official label. We track this in retatrutide FDA approval.