Retatrutide draws more dosage searches than anything else this site tracks, and it is the compound with the least dosage documentation behind it. There is no approved label in the United States or anywhere else. Every milligram figure attached to it traces back to the arm labels of trials, and almost all of those trials belong to one company. The trial record calls it LY3437943; the market shortens it to reta. This is the same page whether you arrived searching for retatrutide or for reta peptide.
This page reports where the numbers come from and what they described. It does not recommend anything and it is not a protocol. Our guide to reading a dosing claim sets out the difference between a labelled figure, a trial figure and a convention, and retatrutide sits squarely in the middle category.
The registry, counted
Checked on ClinicalTrials.gov on 2026-09-09, with retatrutide as the intervention:
| Count | |
|---|---|
| Registrations naming retatrutide | 33 |
| Sponsored by Eli Lilly and Company | 32 |
| Sponsored by anyone else | 1 |
| Phase 3 registrations | 14 |
| Participants planned or enrolled across phase 3 | 25,364 |
| Phase 2 registrations | 4 |
The single non-Lilly registration is NCT07467447, filed by Hudson Biotech. This site has already published what is wrong with that record: it belongs to a set of eight registrations filed by one sponsor at one facility inside a two-week window in February 2026, covering the research-peptide catalogue with tirzepatide and retatrutide appended, none with results posted — and two of the eight carry Eli Lilly's own internal protocol identifiers. Our MOTS-c dosage page works through the verification step by step and it is reproducible in a browser.
So the honest statement of the evidence base is that retatrutide has been studied by its manufacturer, extensively, and by nobody else.
Where 1, 4, 8 and 12 mg come from
The dose figures that circulate for retatrutide are the arm labels of NCT04881760, Lilly's completed phase 2 study in 338 participants with obesity or overweight, protocol identifier 18122. Its arms, as registered:
| Arm | What it administered |
|---|---|
| Placebo | Matched to LY3437943, subcutaneous, once weekly |
| 1 mg | 1 mg once weekly |
| 4 mg (2 mg) | 2 mg starting dose, then 4 mg once weekly |
| 4 mg | 4 mg once weekly |
| 8 mg (2 mg) | 2 mg start, then 4 mg, then 8 mg once weekly |
| 8 mg (4 mg) | 4 mg start, then 8 mg once weekly |
| 12 mg (2 mg) | 2 mg start, then 4 mg, then 8 mg, then 12 mg once weekly |
Two things are visible in that table that disappear when the numbers are quoted as a list.
The first is that the escalation path was itself a variable. The study ran two different routes to 8 mg — one starting at 2 mg and one starting at 4 mg — as separate arms. A trial that treats the way you arrive at a dose as a thing worth randomising is a trial telling you the arrival matters. A figure quoted as "8 mg weekly" does not say which of the two arms it came from.
The second is that 1 mg and 12 mg were not two points on one ladder. The 1 mg arm was administered flat, with no escalation. The 12 mg arm was reached through three intermediate steps. They are not the bottom and top of a single schedule; they are different designs that share a unit.
What the phase 3 programme is doing, and what it has not yet said
Fourteen phase 3 registrations name retatrutide, with 25,364 participants planned or enrolled between them. They include NCT06383390, a 10,000-participant study of cardiovascular and kidney outcomes; NCT07165028, a 4,500-participant master protocol testing multiple agents in metabolic dysfunction, in which retatrutide is one arm among several; and NCT06662383, an 800-participant comparison against tirzepatide that was active and not recruiting on 2026-09-09.
Several have completed — NCT05929066 at 2,335 participants, NCT05882045 at 1,946, NCT05929079 at 1,152 among them. What none of it has produced yet is a label, because a label is the output of a regulatory review rather than of a trial. Until that review happens, there is no dose for retatrutide in the sense that there is a dose for tirzepatide or semaglutide: no recommended starting figure, no maximum, no escalation interval, no indication, no contraindication list attached to a number by an authority.
The practical consequence
The compound is sold widely as a research chemical. What a buyer gets is a vial of stated but unverified content, and a number lifted from a trial arm that was administered under monitoring to a screened population.
Two gaps sit between those two things, and this site covers both. The first is the gap between what a vial is said to contain and what it contains, which is what our certificate-of-analysis guide is about — purity as an area percentage of detected material is not the same quantity as peptide content as a mass fraction of the vial, and a dose calculated from the wrong one is wrong by however much the two differ. The second is the gap between a trial arm and a recommendation, which no amount of testing closes, because it is a question about review rather than about chemistry.
Retatrutide buy-intent questions — where it is sold, by whom, at what price — are outside what this page covers.