What is Reta? Retatrutide explained

The molecule behind the nickname

Retatrutide is a peptide that the pharmaceutical company Eli Lilly is developing under the code LY3437943. The publications describe it as an agonist at three receptors: the receptor for GIP (glucose-dependent insulinotropic polypeptide), the receptor for GLP-1 (glucagon-like peptide 1) and the glucagon receptor. That is why it is often called a triple agonist. The body's own proglucagon gives rise to glucagon, GLP-1 and GLP-2, among other peptides; a hormone or receptor named GLP-3 is not part of the description of retatrutide.

Retatrutide is an investigational medicine. It has been studied in clinical trials in obesity and type 2 diabetes, and the TRIUMPH-5 trial was still listed as ongoing in the registry when we checked the sources. At the source review on 11 November 2026 we found no marketing authorisation for retatrutide. Norway's medicines agency DMP wrote in a decision of 19 June 2026 that retatrutide is not an approved medicine in Norway, and the US Food and Drug Administration (FDA) states on a page updated on 1 October 2026 that retatrutide is not a component of any FDA-approved drug.

What the trials have shown

The results concern the investigational medicine in Lilly's trials, given to specific groups of participants under follow-up. The trials measured body weight and HbA1c, among other outcomes. In the phase 2 obesity trial (338 adults with obesity or overweight, 48 weeks), the average weight reduction was 24.2 % in the highest dose group, versus 2.1 % with placebo. In the phase 3 trial TRIUMPH-1 (2339 adults with obesity without diabetes, 80 weeks) the figures were 25.0 % versus 3.9 %, and in TRIUMPH-2 (1152 adults with overweight or obesity and type 2 diabetes, 80 weeks) 18.8 % versus 5.1 %. In TRANSCEND-T2D-1 (537 adults with type 2 diabetes, 40 weeks), HbA1c fell by 1.94 percentage points in the highest dose group, versus 0.81 with placebo.

The most common adverse events in the trials were gastrointestinal. In TRIUMPH-2, diarrhoea was reported in 27 to 34 % with retatrutide, versus 13 % with placebo, and nausea in 14 to 28 %, versus 8 %. The four trials lasted 40 to 80 weeks and were funded by Lilly. When retatrutide is described online as a weight-loss drug, these measurements of body weight are what is being referred to. The figures cannot be read as the expected effect of another product. The peptide guide goes through each trial with its dose groups, discontinuations and limitations.

• Retatrutide in the peptide guide: trials, side effects and status

Reta and other names

The table shows what the names refer to. The first five rows concern the same molecule. The last two are other active substances that are often mentioned alongside retatrutide.

The difference between the three active substances lies in which receptors they act on. The number of receptors does not say which substance works best. TRIUMPH-5 is the registered trial that compares retatrutide directly with tirzepatide in adults with obesity. At the source review, the registry showed an ongoing trial with no published results.

• Retatrutide compared with tirzepatide

What is sold online as “reta”

Several medicines regulators have warned against products sold online as retatrutide. The UK regulator MHRA wrote on 24 October 2025, after seizing more than 2,000 unlicensed retatrutide and tirzepatide pens, that retatrutide has not been approved for UK use. According to the MHRA, products sold there outside authorised clinical trials that claim to contain retatrutide are likely to be illegal and are potentially dangerous to health. Swissmedic warned on 26 August 2025 against a “retatrutide injection kit” and wrote that the safety, efficacy and quality of such preparations cannot be verified. EMA and HMA warned on 3 September 2025 about a sharp rise in illegal medicines marketed as GLP-1 receptor agonists in the EU. Such products may not contain the claimed active substance or may contain harmful levels of other substances.

In Norway, DMP ordered the holder of a Norwegian website on 19 June 2026 to stop all marketing of retatrutide. The website offered the substance for sale and described it as a peptide for research, with HPLC purity and a certificate of analysis. DMP wrote that retatrutide is a medicine in clinical trials and not an approved medicine in Norway, and that advertising is permitted only for medicines with a marketing authorisation. DMP assessed the activity as unlawful import and unlawful pharmacy activity. The FDA writes that companies have sold unapproved products containing retatrutide, among other substances, directly to consumers with dosing instructions. The products were falsely labelled “for research purposes” or “not for human consumption”, and the FDA has sent warning letters to such sellers. The label alone therefore does not decide how a regulator classifies a product.

A certificate of analysis (COA) describes the sample the laboratory analysed, using the methods stated. It can show HPLC purity and whether the measured mass matches the expected molecule. A purity figure does not say how much peptide a vial contains, and it says nothing about sterility or endotoxins when those tests have not been run. A COA is not an approval either, and it does not turn a powder into the investigational medicine the trials used.

• How to read a COA for peptides

What ArcticAmino sells

ArcticAmino sells retatrutide as lyophilised research material in vials, for laboratory research only (Research Use Only). The material is not a medicine and is not the investigational medicine from Lilly's trials, and it must not be used in humans or animals. ArcticAmino publishes no instructions for use and gives no advice on dosing.

Each batch has batch documentation, and a certificate of analysis (COA) is available on request. The trial results in this article document neither this material nor a particular batch. The product page shows variants and stock status, and the peptide guide gathers the trials, the side effects and the status.

• Retatrutide: product page
• Retatrutide in the peptide guide

Frequently asked questions