Retatrutide explained: what it is, trial status and what is still unknown

What retatrutide is

Retatrutide (development code LY3437943) is an injectable peptide being developed by Eli Lilly. It activates three receptors: GLP-1, GIP and glucagon. People online often call it "reta" or "GLP-3"; the second name is a nickname, not a drug class.

It is being studied for obesity and related conditions. As of this guide, it has not been approved by the FDA or, as far as we have a source for, by any other regulator we checked. On 2 Oct 2026 we searched the FDA Drugs@FDA data, the UK emc compendium, Health Canada's Drug Product Database, the EMA's list of centrally authorised medicines and the Australian ARTG for "retatrutide" and found no approved product in any of them. The FDA also states that retatrutide cannot be used in compounding under federal law.

How it differs from tirzepatide and semaglutide

The added glucagon-receptor activity is the main pharmacological difference from tirzepatide. What that difference adds in people, in benefit and in side effects, is exactly what the phase 3 programme is designed to measure. We will summarize the published results, with citations, on the retatrutide trial page rather than paraphrase press coverage here.

For a side-by-side view of the approved alternatives, see the GLP-1 pipeline guide and our comparisons.

Where the trials stand

Results from TRIUMPH-1, a phase 3 trial, were published on 29 Sep 2026. Phase 3 results are a major step, but they are not an approval: the FDA still has to receive and review an application, which takes time and can end in a request for more data.

The figures above are quoted from the published abstracts and are trial averages, not predictions for an individual. The trial tracker and the legal tracker will date each update.

Side effects: what to expect from the class

Drugs that act on the GLP-1 receptor commonly cause gastrointestinal side effects such as nausea, diarrhea and vomiting, which is why approved drugs in the class start at a low dose and step up. Retatrutide-specific rates and any effects linked to its glucagon activity should come from the trial publications, not from class assumptions.

Our retatrutide side effects page lists trial-reported adverse events with their sources as they are verified.

Dosing and the calculator

Retatrutide has no approved dose because it has no approved use. The doses studied in trials are trial protocol doses, chosen and supervised by investigators. Our retatrutide dosage page reports those trial arms with citations; it does not recommend a dose.

Because research-labelled vials are commonly sold in several sizes, people search for how many units a given amount is. The retatrutide calculator does that arithmetic for any vial size, water volume and syringe, and shows the formula. The math being correct says nothing about whether the contents of an unregulated vial are what the label says.

Why so many people are searching for it

US searches for retatrutide rose 172% year over year in our keyword data (June to August 2026 against the same months of 2025), before the phase 3 results were published. Most of that demand is from people who want to know whether they can get it now, how it compares with tirzepatide and semaglutide, and how to measure research-labelled vials.

The honest answers are short: it is not approved; it differs from tirzepatide by adding glucagon-receptor activity; and the measurement math is the same as for any reconstituted peptide. What is not short is the evidence. That is why the trial figures on this site are taken from the published papers and registry entries rather than from headlines.

Products sold online

If you are interested in retatrutide, the legitimate routes are a clinical trial (searchable on ClinicalTrials.gov) or waiting for an approval decision. If you need treatment now, approved options exist; talk to a licensed clinician.