EP 132:55

Retatrutide, explained: one key, three locks

Name: Retatrutide, explained: one key, three locks
Uploaded: 2026-09-28
Duration: 2 min 55 s
Description: The drug nicknamed GLP-3 is one peptide that turns three receptors. What the trials show so far, what is company data, the new skin-sensation side effect, and why it is not approved.

The drug nicknamed GLP-3 is one peptide that turns three receptors. What the trials show so far, what is company data, the new skin-sensation side effect, and why it is not approved.

Transcript and sources

Online, people call it GLP-3. It's actually retatrutide: one molecule built to turn three locks at once. Here's what it does, what the trials show, and what's still unknown.
Retatrutide is a single peptide made by Eli Lilly that activates three receptors: GIP, GLP-1 and glucagon. It's thirty-nine amino acids long, with a fatty tail that lets it ride on albumin, so its half-life is about six days.
Count the locks. Semaglutide turns one. Tirzepatide turns two. Retatrutide turns three. That's all GLP-3 means: it's a nickname, and there's no hormone by that name.
The locks don't turn equally. In lab tests, it's about nine times stronger than the body's own GIP at the GIP receptor, and weaker than natural GLP-1 and glucagon at theirs.
The strange one is glucagon. It normally tells the liver to release sugar, so why add it? In mice, the glucagon part raised energy burn, while the other two cut food intake. And in people, adding GLP-1 cancelled that rise in sugar: in retatrutide's diabetes trials, blood sugar went down, not up.
One of the most striking results was in the liver. In a sub-study, liver fat fell by about eighty-two percent in twenty-four weeks on the top dose.
In the phase 2 obesity trial, the top dose averaged twenty-four point two percent weight loss at forty-eight weeks, if everyone had stayed on treatment.
Then the first big phase 3 trial, TRIUMPH-1. At eighty weeks, the top dose averaged twenty-five percent weight loss, counting everyone. But those numbers come from Lilly and a conference talk; there's no journal paper yet.
The side effects look familiar. Nausea hit about four in ten people on the top dose, and about one in nine stopped because of side effects, versus about one in twenty on placebo.
One side effect is new. Some people reported odd or unpleasant skin sensations, called dysesthesia: up to about one in five on the top dose in one trial, versus under one percent on placebo. Why it happens isn't known yet.
Retatrutide isn't approved anywhere. Lilly plans to apply to the FDA in the first quarter of 2027. And the FDA has sent warning letters to sellers of research-use-only retatrutide, calling it an unapproved drug.
One key, three locks, and a lot still unknown. Every trial is on the GLP-1 guide at peplexicon.com.

Sources